2002 Chevrolet Monte Carlo

A bright yellow 2002 Chevrolet Monte Carlo 3.8 liter with 117,263 miles on the odometer is at Mr. T's shop. The vehicle came in as a no start, no crank condition. The battery load tested bad so a new battery went in with the same result. I am informed that they can jump out the starter relay and the car will crank but will not stay running. Let's look at the starter circuit for starters.

Ok we have a starter relay which is called out as a crank relay in this diagram. The relay is PCM controlled. The PCM will engage the relay when it sees a crank voltage input and the gear input is correct. We don't want the vehicle cranking when in gear. But, there is one more piece of the puzzle. Lets look at some theory.

This is some Passlock (the vehicle theft system) theory from GM. I underlined the parts that pertain to our issue at hand. Passlock has been around since 1995/1996 on GM vehicles. On some years/models it will disable the starter relay operation and other years it won't. Check the description of operation if you are not sure. I know what I am doing next.

I hook up my Tech2 and perform a Class 2 DTC check. I use this to see what modules are reporting on the Class 2 data line. I see an issue here already. There is a module that is linked to our problem that is not here. The BCM is AWOL. Now, we have to find out why. I check the fuses that power up the BCM in the left side instrument panel fusebox which are good. My next step is to see if there is any add on items such as an aftermarket alarm that would be causing issues with the BCM.

The BCM is located under the left side of the dash buried up high. There is an aftermarket alarm involved that dropped on me as I dropped this panel. I disconnected the aftermarket alarm module and rechecked to see if the BCM came back online. No dice. We have to get right at the BCM.

There it is tucked up high. I wrestle it down and backprobed the powers and grounds right at the BCM they are fine. The next thing I do is to disconnect all the connectors at the BCM and walk away from the vehicle for 20 minutes. I return and reconnect the BCM. Let's recheck to see if now the BCM is reporting.

Well look at this. The BCM is back online. The car starts and runs now. This is what is called "logic lock" in the industry. The module was electrically locked and shutdown. Disconnecting it for 20 minutes and reconnecting unlocked it. I have seen this on Chrysler and Nissan vehicles as well as GM vehicles. There is much debate about what causes this and what is the proper repair. I believe logic lock is caused by voltage fluctuations, surges, spikes, or excessive ac voltage ripple. In this case I believe the weak battery caused the logic lock. I did check charging rate and for ac ripple as well. Now, the proper repair some believe would be to change the locked module for fear it will lock again. The theory there is that the module lock is a symptom of a bad module. I give the shop owner the options. He decides to let it go as is and to inform the customer of the possibilities. This vehicle has been out now for a month and doing just fine.

2001 Nissan Sentra

This 2001 Nissan Sentra 1.8 liter with 216,173 miles on it rolled into this shop with the MIL on and running rough. The car's owner "diagnosed" it as a bad fuel injector because he had trouble with injectors before. The shop owner called me in to confirm or disprove the customers "driveway diagnosis". I start the car up and indeed it runs rough and has a MIL on. Lets check the code for starters and then roll up the sleeves.

Ok, we got something to go on. I have a P0303 code for cylinder #3 misfire. I am thankful for this because Nissan on the whole usually sets a P0300 code for multiple misfires rather than specific cylinders. Either way we need to confirm if the PCM is telling the truth about which cylinder is misfiring and then find out why it is misfiring. Whenever possible I like to backup what the PCM is telling me. So......

My scanner allows me to do a power balance test. When I select a cylinder I can disable that cylinder and check for contribution. I am looking for rpm drop when the cylinder is killed and I am looking to feel the engine running change as the cylinder is disabled. Here I disable #3 cylinder and the rpm doesn't drop and I do not feel any change in how the vehicle is running. I always try a known good cylinder to compare and check whether my scanner is doing as advertised.

Here I do the same procedure with #1 cylinder. I get a substantial rpm drop and the vehicle runs much differently with #1 cylinder disabled. So, now we know we have a true blue problem with #3 cylinder. What's next?

This Sentra is a California emissions vehicle. It uses two upstream oxygen sensors to monitor fuel control. Oxygen sensor 1 is bank 1 that monitors cylinders #1 and #4. Oxygen sensor 2 is bank 2 that monitors cylinders #2 and #3. Important to know when we look at fuel trims. Just a FYI there was a CA (Clean Air) version that had one Air Fuel ratio sensor upstream instead of two oxygen sensors. Know which emission standard you have when doing testing.

Here are the fuel trims for this vehicle at an idle. Nissan uses what is called Alpha for fuel trim. Basically 0 Alpha is perfect fuel control. Nissan actually displays true 0 Alpha as 100. The Ottotest interprets it a bit differently. But, it serves the purpose. Whenever I have a misfire I always look at fuel trims. They can give you clues to where to go next and zero in on your problem. Remember, my job is to diagnose quickly and accurately. I see nothing here that would tell me that this vehicle suffers from a fuel injector issue. If the fuel injector was plugged or inoperative I would expect to see exaggerated numbers in the positive range as the PCM tries to compensate for the lack of fuel. The exact opposite would happen if the injector was leaking. At this point I am not looking at a fuel related misfire.

Those of you that know how I operate should not be suprised by the next step. Out comes the scope and low amp probe. I need to look at the ignition system. This year utilized 4 COP (Coil on plug) units. First our problem cylinder.

Yeesh! Here we have a textbook example of a shorted coil. The turn on portion of the pattern goes straight up. No turn on oscillations at the beginning of the pattern (more on primary current and turn on oscillations later this month). Let's check a known good cylinder.

Notice the difference. A nice sloping turn on with turn on oscillations at the very beginning of the turn on pattern. This vehicle has a bad COP unit on #3 cylinder. Let's check that #3 injector to satisfy the customer and shop owner.

Looks good to me. Nice pattern with about 4.0ms of on time. A nice injector turn off spike and we know it is not clogged due to the "pintle hump". Let me point out the pintle hump.

This is the pintle hump. This is the actual mechanical closing of the injector viewed through the scope. No pintle hump and typically the injector is clogged or damaged mechanically. Some pintle hump injector patterns will not be so defined. It is something I look at when looking at injector scope patterns. I inform the shop owner to get a quality COP unit and spark plug for #3 cylinder. I also advise to check the rest of the plugs as well.

 Just to go the low tech route as well I put my open gap style spark tester on #3 COP unit start the vehicle and we have no spark.

More pictures of "chia pet" modules

Remember last time when I told you about another van that had an EPA issue. Well here it is after the shop helper cleaned it with some bleach. Remember, this is after!

Here is the vinyl mat lifted up. The helper did an excellent job of cleaning. This vehicle is going to need at the very least a new SDM, setup, and repair of the rotted harness.

2002 GMC Savana 2500 Diesel

Ok. Let me start off by apologizing for not posting in awhile. I have been very busy thankfully. I will be updating more often. I have here a nice 2002 GMC Savana 6.5 liter diesel van with 99,859 on the odometer. I am called in after this shop put a motor in and wants to set injector pump timing. They hook up the shop scanner and get no communication. That is when they called me in. I get the same result with my Tech2 scantool. The vehicle starts and runs, so I know something is going on. I poll the modules with my Tech2 and can only communicate with the vehicle theft deterrent module. Lets look at how this system works.

This system utilizes what is called Class 2 communication. Think of it like a telephone line. This line is where modules communicate with each other and with a technician through pin #2 of the data link connector. Each module on Class 2 has the ability to communicate all on it's own. It is what is known as a peer to peer system. It doesn't need a "master" module to work.

Here, I circled the players involved on this vehicle. Since I can communicate with the theft module I know I have some Class 2 communication. I have been down this road before. There are two common modules I see that cause Class 2 issues. They are the ABS module, the SRS (Air Bag) module, and their related wiring. The quick and dirty on these problems is disconnect modules one at a time and see if the remaining modules start talking. So, I put the van up in the air and disconnect the ABS module on the frame rail and recheck Class 2 comunication-no dice. Still only the vehicle theft module reporting.

   Now, the SRS module is under the drivers seat. Here is a shot from the passenger side. GM puts a one piece vinyl mat down throughout the front floor of these vehicles. This mat goes under the seats and over the the top of the SRS module. This vinyl mat is great for holding moisture underneath it. These vans all have water intrusion issues. If the fusebox and PCM isn't filling up with water, the windshield is leaking and causing water to collect especially under the driver's seat. So, we are left with taking the front seats out and peeling the vinyl mat back or slitting the mat around the SRS module with a razor to do some inspection. I get the ok to slice and dice and this is what I see.

Holy corrosion! I have seen these pretty bad, but this by far was the worst. The SDM (Sensing and Diagnostic Module) and it's connector are chia pets! Here is another shot.

I try to disconnect the connector from the SDM and will not budge. In fact, the shell comes off in my hand and the terminals are corroded to the module. Hard decisions need to be made here. I will have to cut this harness to see if we get communication back. I also give a sneak peek to the harness that is running back from the SDM to the front as they frequently corrode as well from trapped moisture. It doesn't look that bad, so I snip the SDM harness and now we have 5 modules reporting on Class 2. SDM, PCM, Radio, Vehicle Theft, and ABS. Now, that I am able to communicate with the PCM we check and adjust injector pump timing as per GM specifications.

Here is a scope pattern of Class 2 after we snipped trhe SDM harness and got the other modules back on line. I should have taken a capture before snipping the SDM harness. I guarantee you that it didn't look anything like this. This is a nice healthy Class 2 pattern. Nice well defined square waves that are 7 volts in amplitude and are off ground approximately 200mv for less noise. The square waves come in "data packets" as modules send signals to one another. What is funny is that the week before this job I was at another shop with a similiar problem. Someone had an aftermarket radio shoved in it and I was very suspicious that the shoddy radio install was causing issues. I pulled the radio out and was shining a light in there and noticed strong evidence of rodents-seeds, acorns, droppings, and chewed wires. Still shining my light in this area I was also greeted by roaches! At this point I fled the vehicle and informed the shop owner he needed an exterminator for the vermin and roach problem his customers van had. The next day another shop had van issues and lifting up the vinyl floor mat revealed a rotted harness and black stringy mold. At that point I informed the shop owner he had a EPA issue with that van. You never know what you are going to find.   

The Future

This past week I was invited to sit in on an advisory panel for Lincoln Technical Institute in Whitestone, Queens. The purpose of this panel was to tour the school and offer feedback on the program. The facility is state of the art and the program is an excellent start for young technicians wanting to get into the business. I was honored to be asked for my opinion on various subjects during the feedback sessions. Just wanted to say thank you to the people over at Lincoln Tech for the invite. I am hopeful for the future of the automotive industry and the automotive technician.
Speaking of the future and feedback. I am at the seven month mark with my Ottotest scantool. Look for an unabashed detailed review of this scantool real soon. Future articles also include more fun with a low amp probe including more fuel pump patterns as well as checking ignition low amp patterns. Also, a blast from the past Lexus odyssey, GM Class 2 issues caused by a "chia pet", an Audi evap issue, and two similiar Caravans with different end results. I think I will also detail a "day in the life" of a mobile diagnostic guy like myself. Any suggestions for articles? Feel free. 

Drivers Seat Diagnostics-2004 Toyota Tacoma

Here is one 2004 Toyota Tacoma 2.4 liter with 145,763 miles on the clock. Vehicle was towed in as a crank no start. On Motormouth radio the hosts were asking me about "Drivers seat diagnostics". I wanted to use this vehicle as an example of what can be done exclusively from the drivers seat in short order. Remember, in my job I need to diagnose accurately and quickly. The first thing I do is crank the engine over and verify it is a no start. I also listen to make sure we have an even cranking speed. It is indeed a no start and cranking speed is nice and even. Time elapsed-2 minutes. Next step is to hook up the scantool to look at some data parameters while cranking.

So here is a screenshot from my Ottotest. I am looking at engine rpm, fuel pump relay activation, injector pulse, and mass air flow sensor grams per second. The screen is 25 seconds worth of cranking data captured. Including scantool boot up we are up to approximately 5 minutes. Lets zoom in and add some cursors.

Ok, now we are rolling. We have 209 rpm, fuel pump relay is being activated, 12ms of injector pulse, and the mass air flow sensor is reporting 4 grams per second. So what does this all tell us. To me the injector pulse and fuel pump relay activation tells me we do not have an anti theft issue causing the no start. Most manufacturers turn off injector pulse and fuel pump operation when in theft prevention mode. The 209 rpm tells me that my crankshaft sensor is working. The 4 grams per second cranking tells me this engine is mechanically sound. If there was an issue with valve timing/compression it would affect our cranking engine vacuum and therefore we would have lower MAF data cranking. Also, remember our cranking speed was even in our very first step. Time elapsed now-7 minutes. Let's move the cursor.

Wow. We went from 12ms to 33ms of injector pulse. This is something I see all the time with Asian import vehicles. If the car doesn't start with the base injector pulse lets double or even triple it. At this point if this vehicle was dumping this much fuel there would be two things happening. Number one I would smell fuel and number two the engine would crank over faster due to washed down cylinders. Cranking speed did not increase either by scantool values or my ears. I also do not smell any fuel. Time elapsed-8 minutes. Keep moving.

I look at a wiring diagram and locater for the fuel pump relay and break out the low amp probe. The next shot gives you an idea where it is.

I told you this was "Drivers seat diagnostics". At this point I am at the 10 minute mark into my diagnosis. Checking actual fuel pressure on a Toyota product is asking yourself to be tortured. Typically, you have to break the pressure line open and piggyback an adaptor and get a reading. Put it back together and pray it doesn't leak. I would rather look at an amp pattern and see if I can decipher something from there.

This is a nice even pattern. However, the amperage is way too low and the fuel pump RPM (revolutions per minute) is 7741rpm which is too high. Most fuel pumps have eight bars or sections. The way that we figure rpm is identify the eight segments and then setup cursors to time one complete revolution of the fuel pump. Which in this case was 7.75ms. We then take this time measurement and divide into 60,000. This gives us our fuel pump speed. Using amperage, pattern, and fuel pump speed we can determine if our issue is fuel pump related. While there are no hard and fast rules for amperage and speed. I use this as a guideline. Most fuel injected pumps draw between 5-7 amps and 5,000-6,000 rpm is the norm. Now, there are exceptions. One that comes to my mind is GM vortec fuel pumps that draw 9 amps all day long on a healthy pump. Back to our Toyota. Low amperage and higher than normal rpm tells me we are out of gas in the tank or the pump is freespinning. I wrap on the tank and there is fuel in there. So that leaves the pump is freespinning. To verify all of this I pop the hood and give a spritz of carburetor spray into the air duct and the vehicle starts and runs until the carburetor spray is gone. The tank has to come down. Time elapsed-12 minutes.

There it is fresh out of the tank. We have a fuel pump that become dislodged from the rubber hose that connects it to the vehicle's fuel system. So we had a fuel pump pumping fuel back into the tank instead of to the fuel system.

 
Here is another shot. The squeeze clamp that holds the fuel pump output tube to the rubber hose seemed to be in fine shape. I have seen this once before on a Toyota pickup truck that was used for heavy off roading and I theorized the jostling around caused it. But, this is a street vehicle. With well over 100k miles on it a new pump was installed with all new attaching parts.

   New pump and the vehicle starts and runs.That is more like it. The amperage is back to normal at just under 8 amps. But, wait the rpm is still high. If you figure the rpm it is at 8915rpm and the pattern is not exactly textbook. This is just a cheap aftermarket pump. It is an issue that is rampant in our business unfortunately. I feel a rant coming on. However, the focus of this case study was to show how "Drivers seat diagnostics" can work. So, in just over 12 minutes without getting our hands "dirty" this vehicle was diagnosed. Now, remember there are a couple of items you need to have for this to work. One is faith in your scantool and the other is a working understanding of the make and model you are working on.   

This Sunday

I will be a guest on this Sunday's Motormouth radio show from 12pm to 1pm. Along with my good friend Joey "Bag O Donuts". The hosts Ray and Chris always put on quite the show and I am grateful for the invite. You can tune in through http://www.motormouthradio.com/ or locally at 90.3 WHPC-FM. It is always a good time with these guys and you can call in and ask questions, make comments, etc. The topics can range from muscle cars to hybrid technology. You never know and that is what makes it so much fun. So tune in.

Jeeps, Jeeps, and more Jeeps....

It always seems that you get a run on things in the automotive world. In a shop you can go months without doing a single heater core or water pump and then that is all you are doing for the next week. I have had a run on Jeeps lately. Here are three examples.
First up is an oldie, a 1993 Jeep Wrangler 4.0 liter that is lifted and obviously been repainted at least once in it's lifetime. This shop called me in because of a short circuit. This vehicle is blowing the #9 fuse in the interior fusebox as soon as you put one in and turn the key on. I do a fair amount of electrical issues. I am not always knee deep in check engine lights and drivability issues. Shorts and battery drains are always fun. The first thing I always look for with shorts and drains is aftermarket equipment such as alarms and stereos. This vehicle has an aftermarket stereo. A quick unplug of the stereo and we still have a short. So we can cross off the aftermarket equipment. Next I pull a wiring diagram and get the "lay of the land" of the circuit.

Here it is. Circuit G5 Dark Blue with a White stripe. It feeds plenty. The diamond shaped box with G5 in it is a splice joint. This splice joint is behind the instrument cluster. Sometimes, I will get to the splice joint and take it apart to narrow down my search. In this case it is too much work at this point. I always go with the easier items first. I disconnect the buzzer module which is right at the fusebox-no luck. I need to divide and conquer here in a hurry. I disconnect the bulkhead connector to determine whether the short is on the inside or the outside of the vehicle. With the bulkhead connector hanging in the breeze we still have the short. But, we have narrowed it down to the interior. So we are left with the rear defrost relay which this doesn't have but sometimes they will have the connector and the instrument cluster, indicator lamps, and the gauge package. A quick look for a rear defrost relay connector yield nothing. Looks like someone has been into the dash wiring. I remove the instrument cluster connector and the short is gone. Do we have a shorted cluster? Reconnecting the cluster and we still do not have a short. This is definitely a wiring issue and I moved the "short" when I pulled the cluster connector. Lets look at that instrument cluster connector again.

I twist the harness around 180 degrees and there she is. A rub through. The Dark Blue with White wire was rubbing on a dashboard support bracket when plugged into the cluster and grounding out blowing the fuse. The original factory strap was missing. I taped up the wire, taped the harness, and secured it with a couple of tie straps. Next....

This a 1996 Jeep Grand Cherokee 5.2 liter with 156,814 on the odometer. This vehicle has a lack of power on heavy acceleration. This vehicle has had a remanufactured motor, rebuilt distributor, and a tune up recently. The problem has been there prior to all this work as well. At this point this shop just wants this vehicle fixed and gone. I give it a quick visual and all looks well. I start the vehicle up and runs pretty good just sitting there. I hook up my scanner check codes-there are none. I dial in some pids I want to look at and head out on the road.

I am looking at Engine RPM, MAP, Upstream O2 Sensor, and Throttle Position. I head out and the vehicle runs pretty good out on the road. I really lean into the throttle and this vehicle noses over, bucks, and shakes. Let off the throttle and it recovers. In fact if you just drove it around normally you would think it ran great. I get back to the shop and concentrate on the part of my road test at heavy throttle.

I blew up the portion of the graph and added a cursor. O2 sensor voltage plummets on heavy throttle. If you asked me to diagnose this car without scan data I would have said this thing had a bad crankshaft sensor or bent flywheel. I would have never suspected fuel. But, this is why we do the testing.

I knew we were on to something when I hooked up my fuel pressure gauge and the engine stalled. Restarted the vehicle and have 50psi engine running at an idle. This returnless fuel system should have 49psi all the time idle, cruise, wide open throttle. So far so good as far as pressure.

I flash the throttle and the fuel pressure drops like a rock. Here I caught it at15 psi. Hardly what we should see. I open up my volume knob on my gauge and the fuel just dribbles out and the engine stalls. When these returnless systems have this condition they tend to aerate the fuel which can also setup misfire codes as well. The aerated fuel makes it to the injectors and causes a misfire until the air is purged with good fuel flow.

A check with a low amp probe reveals a pretty decent pattern and decent amp flow at 5 amps. At this point I know I do not have a connection issue or an available voltage issue. I suspect an issue with the in tank fuel filter or strainer. I tell the shop to drop the tank and with this mileage replace the fuel pump module assembly which includes pump, filter, and attaching parts. All is well after the pump module replacement and runs well under heavy acceleration.

Our final Jeep is a 2006 Wrangler 4.0 liter with 59,564 miles on it. It was in this shop for some type of crankshaft sensor code. The customer supplied the crankshaft sensor and the shop installed it and we still had a code. I hook up my DRB3 scantool and retrieve a code P0016 that is current. Lets look at the code set criteria for a P0016.

Remember, to click on images so you can read them. Well not very particular in their code set criteria. How much out of phase before the code sets? There is a pid called Cam/Crank Difference. It has a value in degrees. mine is sitting at 14.6 degrees. Experience has shown me anything 8 degrees and better is an issue. Obviously, we would like it as close to zero as possible. Over the years timing chain/belt and gear wear cause this to wander. Service information gives you no adjustment procedure other than the cam sensor housing initial installation. Did someone do some motor work on this Jeep? A call to the customer confirms that there was no motor work done. The call also helps me with my path of diagnostics. When I ask the customer if there are any drivability issues with this vehicle he tells me "Oh yeah it breaks up over like 3500 rpm's." Thorough interrogation of the customer and their problem is essential in this business. It is amazing what you can find out through a few short moments with the customer asking the right questions. Onward. Now we know it also has a drivability issue as well. My next step is to scope the cam and crank sensors in dual trace to check their actual relationship.

I use two markers in looking at Chrysler NGC (New Generation Controller) 6 cylinder cam and crank relationship patterns. The NGC patterns are much different than the old SBEC (Single Board Engine Controller) or the JTEC (Jeep Truck Engine Controller) patterns. You have to know your enemy thoroughly. Thankfully every NGC 4 cylinder looks the same, every 6 cylinder looks the same, etc. 

These are my two markers that I use. First up is the single cam pulse that occurs after the double pulse. The rising edge of this pulse should occur right after the second pulse after the high (5 volts) "signature" notch of the crankshaft sensor signal. In the above example it is occuring somewhere between the third and fourth pulse after the signature notch. The other marker I use is the triple pulse of the camshaft. I normally see the the middle pulse on the pulse of three ocurring somewhat close to the middle (actually a bit to the right) of the low (ground) "signature" pulse. Here you can see it is ocurring at the first pulse after the low "signature" pulse. So we know we are off, the scan data was telling us as well. The scope confirms it. So, now what? I have seen plenty of cam/crank relationship errors caused by cheap aftermarket crankshaft or camshaft sensors, bad flywheels, timing belt/chain stretch, etc. Normally, when I see a broken flywheel the patterns are shifted in the opposite direction. I look down at the camshaft sensor and it's housing. Service information says when the cam sensor housing is installed correctly the cam sensor will be at the 4 o'clock position looking over the right front fender. Hmm. mine looks a bit off. Mine looks more like 5 o'clock. Now there is no factory adjustment procedure to adjust. Only to install. Let's go for it!

 I  loosen the holdown and swing it to approximately 4 o'clock. Lets see what our scan data shows and then we can fine tune it with the scope.

Not bad at 3 degrees. I can live with that. Now what about our scope pattern?

       Wow! Spot on! Look at the markers I discussed earlier. I clear the code and relearn the cam/crank  values with the scantool. Which should be done if there is any sensor replacement or adjustment. I start the vehicle repeatedly to make sure we have no more MIL lamp. Recheck values and road test. I am happy to report the Jeep pulled hard all the way up to 6000 rpm. So now the question is why was the cam/crank relationship so far off? Well, I believe there was "Hotrod Harry" mentality at play here. The owner of the Jeep and his friends like to "play" with cars. I believe maybe one of them thought by altering the position of the cam sensor housing he was gaining horsepower or something like that. The bolt at the holdown looked like there was someone there prior. The other explanation is that it is not uncommon for the gear at the bottom of the cam sensor housing to wear a bit. I advise the shop owner of my thoughts on why cam/crank relationship was out and marked with a paint pen on the cam sensor housing and block two witness marks to alert me to anymore "reengineering".