2001 Cadillac Seville SLS

There she is. One 2001 Cadillac Seville SLS with 103,361 miles on it. Pretty clean car. Unfortunately, it does not start, nor crank, nor does the host of electronic gadgetry on this car work. The owner says sometimes he can disconnect the battery and reconnect and vehicle it will start and perform well. Notice the battery charger in the picture. Usually, a clear indication to me that the battery in the car is a paperweight. I see a ton of bad batteries. People will have expensive stereo systems, fancy alarms, and they have a bad battery. They don't mind jumping the car 5 times a week. That spells disaster to electronics. Between, voltage spikes and the eventual backwards jump start it gets ugly fast. Let's get the show on the road with this car.

I hook my Tech2 to see what modules are reporting. I choose Class 2 DTC Check to see what is going on quickly.

This is what I get. Now, this could go many ways here. These vehicles have lots of issues. Bad ignition switches, water leaks soaking modules and causing communication issues. On this model I know that they typically will have windshield and/or passenger door leaks and the SRS (Airbag) module under the passenger seat gets soaked and causes issues. A quick feel under the seat and it feels pretty dry. I then break out the scope and check pin #2 at the DLC and get a constant 12v. The Class 2 communication line is shorted to power. So many things can cause this-bad modules, shorted harnesses, poor grounds. Lets look at the Class 2 line.

Here is part 1.....

Here is part 2. Lots of modules here which is to be expected on a Cadillac. These modules are arranged in a Loop pattern. GM has 3 different ways to arrange Class 2. Loop is what you see here where communication lines go in and out of every module. Star arrangement where each module generally has one communication wire going to it and there is usually a splice pack where you can take one module off at a time. Finally there is Star/Loop which combines the two. Loop is great for redundancy but can be a little more intensive to diagnose. I like to start with easy. I visually check grounds and harnesses for rubbing or damage. They look pretty good. Next, I start disconnecting modules, cycle key and then look at my scope on Class 2 for activity. I disconnect ABS no luck. Every other module is buried except one-the PCM.

I unearth it and disconnect both connectors.

This is what I have at pin #2 at the DLC now. Perfect Class 2 waveform. Let's recheck the modules with the Tech2.

Nice! I now have modules reporting. The only module not reporting is the PCM. Obviously, it is hanging in the breeze. A quick check of powers, grounds, and 5vref at the PCM reveals no other issues. This PCM is the cause of the Class 2 being shorted to power. Remember, the battery charger, etc. I inform the shop owner of my findings and give him options so he can discuss with this customer. He calls me the next day and tells me money is tight with the customer. He wants to go with a used PCM and still does not want to change the battery. I do not mind setting up used modules as long as it will not cause issues. Be careful. Sometimes replacement of used modules will cause issues. Ask one shop I got called in when they changed a BCM (Body Control Module) on a Caravan to fix a rear wiper issue. Well after the used BCM went in the vehicle got infected with VTSS (Anti theft) and the mileage almost doubled with no going back. Try explaining that to the customer. Be careful! All my customers know to call me first and ask me about used module beforehand. It is something I preach. Ok, so we are going to be putting a used PCM in this Cadillac. New, reman, or used it will have to be setup with proper VIN and calibration. As well as the theft system relearned.

Used PCM installed. Still have great communication. Next....

I hook up my Midtronics battery maintainer to the battery. Not because this vehicle has a bad battery. I will not reflash, program, etc without it. It is a ripple free battery maintainer that holds voltage steady at 13.4v. It is endorsed by GM and has been the industry mainstay for some time. I know guys that flash with jumpacks or battery chargers. I do not have that kind of luck. There is a lot of data being transferred and I want to make sure I have done everything for a successful flash event. A quick check with my DVOM at the battery tells me we have stable proper voltage. Next, I hook up the Tech2 and request info from the used PCM. It will have the VIN and calibrations from whatever vehicle it came out of. I will be overwriting that with proper VIN and calibrations for this vehicle.

I then hook up my Tech2 to my TIS2000 program, input the proper VIN and choose replace and reprogram PCM. This is what is called remote programming. It is when you are downloading calibrations to the Tech2  from the laptop then disconnecting and using the Tech2 stand alone to update programming. Sometimes I use this method other times I use pass thru. I avoid flashing/reprogramming with a J2534 tool whenever possible. I like factory tooling. Less pitfalls and suprises.

There are the correct calibrations. I upload to the Tech 2 and go back to the car.

Here is where it gets a little dicey. These Cadillacs along with certain Corvette models (check your service information) really should be programmed by themselves. Apparently, with so many modules on the communication line if one of them "talked" while a programming event was going on it could corrupt the programming. So GM recommends to reprogram these PCM's with a special stand alone harness that isolates the PCM. Others, I know have made jumper harnesses of their own to work around this. I had some good information that if I pulled the I/P fuse in the underhood fusebox that the chatty modules involved would go to sleep and I could program this PCM. So I did.

Here I rechecked. Sure enough my chatty modules are no longer reporting and the PCM is there. A quick recheck of proper voltage and connections. Lets program!

Here we go.

A couple of minutes later. Lets recheck for proper calibrations.

Bingo. Vehicle still is not going to start. We need to relearn theft.

Here we have a choice to relearn theft. GM typically gives you two choices. One is a long way typically 30 minutes which involves turning key on and waiting, etc. The second way is a program that will run that speeds things up. That is what I use. Again, we request info from vehicle using the Tech2. This time VIN is correct.

I choose theft relearn and upload it to my Tech2.

This is a lot faster. After completion the vehicle starts and runs properly. I clear all codes and make sure to perform any after reprogramming procedures such as oil life reset, crankshaft variation relearn, etc. The Cadillac rides again. Hopefully, that battery gets changed sooner rather than later.