[V-SER1ES]

Hey everyone, first off, just want to thank you for all of the knowledge shared on the site. I have done some searching and found some wire schematics, but hoped someone might have some input.

2006 STS-V 4.4L w/Keyless Ignition and Passive Entry, but I believe the system is the same as 4.6L/3.6L.

The car hasn't been driven in a few months, but I have had a battery tender on it since parked, and I start it (with the tender unplugged) about once a month.

Yesterday when I went to start it, it was no crank/no click/no start. Battery voltage 12.9 and load tested in the 80% range. The door opens normally with the key fob in pocket, and all controls are normal upon entry. When I put my foot on the brake, normal "Press Brake Pedal and Push Start Button to Start" appears in IP. When I press Start, everything on the dash goes dark. No warning lights, no backlights. I do get the passenger airbag light cycle through its normal sequence. I believe the dome lights stay on though, as the driver door was open. Also, as soon as I press the start button, the peanut lights in the headlights come on and stay on just like they would if the engine was running. There is NO audible click from the starter solenoid (possibly not even starter relay, was too far away to tell) when start button is pressed. There was also no significant change in battery voltage when attempting to start. When I push the off button on the ignition, the twilight sentinel headlights/taillights come on for a few moments like they normally do.

I have heard that battery connections can sometimes get loose or that battery voltage could be an issue. I tightened both terminals at the battery (which were tight) and hooked a known good jump box to the battery as well to try again. With the jump box on, I registered 14.4V at the battery before starting. When hitting the start button, the voltage didn't drop any noticeable amount either. No change in symptoms. I turned the ignition off again and this time placed my key fob in the compartment inside the center console (tried both directions) and repeated test. No change. Finally, I placed the gear lever in neutral and repeated, and then park again and repeated. No change.

My next step will be to begin looking for voltage at the starter relay. Has anyone had experience with this situation on these cars? Any help is appreciated!

 

[CWB]

Look up the "purple wire trick" on this forum. Go through those procedures. The "pwt" bypasses all safety interlocks so be SURE car is in park or it may jump forward unexpectedly. Possible causes of your problem include:
1. loose connection at the starter
2. Bad starter and/or solenoid
3. internally corroded positive wire from battery to starter
4. Bad starter relay
5. Bad wiring to or from starter relay (4 wires)
6. Bad ground connection at any of several locations on the car
7. Bad starter push button on the dash
8. Any of several computer commands that interlock the starting system and keep the starter relay from getting the start signal
The "pwt" will eliminate 1,2,3 (or focus your attention on these 3) with no purchases or disassembly required. I am eliminating the battery for now due to the "no drop in voltage at all" on start attempt but I have seen many problems lead to the battery unexpectedly. The 80% is not the best reading for a battery that has been on a tender for weeks/months. Good Luck

 

[V-SER1ES]

The "pwt" will eliminate 1,2,3 (or focus your attention on these 3) with no purchases or disassembly required. I am eliminating the battery for now due to the "no drop in voltage at all" on start attempt but I have seen many problems lead to the battery unexpectedly. The 80% is not the best reading for a battery that has been on a tender for weeks/months. Good Luck

Thank you! I will be sure to update this thread when I have time to use this trick for diagnosis. In the meantime, I should be looking for a new battery....OUCH on their prices these days.

 

[Submariner409]

Anything up in the dedicated STS-V forum ?

STS-V Series Forum - 2006-2009

Forum for discussion of the Cadillac STS-V, a high-performance executive sedan based on the Sigma platform and powered by a 469bhp supercharged LC3 V8.

www.cadillacforums.com

Yep, good batteries have gotten expensive - just replaced the Exide in the 2002 STS last Friday.

 

[V-SER1ES]

UPDATES

Anything up in the dedicated STS-V forum ?

Not that I could find with a search of all subforums - although I could be overlooking something.

Look up the "purple wire trick" on this forum. Go through those procedures. The "pwt" bypasses all safety interlocks so be SURE car is in park or it may jump forward unexpectedly. Possible causes of your problem include:

Okay, so here is where I began my diagnostics. Upon close inspection beside the battery, there was a small amount of 'mouse home material' that I took time to clean, vacuum, and inspect around. There are several large wire harnesses in this area - and most of them had some age cracking of the taped shell that made it hard to find rodent bites. However, there was one pretty apparent fray from chewing on this wire near a connector, which I believe may be the pink wire going from the fuse panel (starter relay) to the starter.

Before repairing it, I disconnected the battery and inspected the terminals. They were tight on the battery to begin with and this is the condition after disconnecting:

The backside of the screws were in great shape too. I don't believe the connections to be an issue here.

I then removed the battery and tray and vacuumed and inspected around it and underneath it. Everything was in good shape. I made the repair of the pink wire - a solid crimp butt connector with two layers of heat-shrink tubing. I didn't take a pic of that.

After another inspection and not seeing any other visible broken/exposed wiring, I dropped the battery back in and reconnected it. Verified that I had 12v at the terminals as well as in the fuse panel. I crossed fingers and put ignition to start...no change. Same symptoms.

In the underhood fuse panel, I located the starter relay. I did the 'purple wire trick' by using my relay tester/switch.

The ignition button on the dash allows you to place the ignition in 'run' by pressing down on the 'acc' side of the rocker for 5 seconds. This energizes the IP and modules as if the vehicle was running. In this position, I checked each leg of the relay...one side had 12v and ground, the other had 12v and an open circuit (which it should, switched ground supply by the PCM). Flipping the switch on the relay tool energized the starter, which cranks as it should.

So, the starter side of the equation is in working order. It appears the PCM isn't sending ground to the starter when it is called for. I also tried starting in Neutral as well as Park...no change. I also don't recall hearing the fuel pump engage as it normally does. IIRC, it usually would come on when the driver door was opened?

To recap, when you open the door you are greeted by the normal things. When you put your foot on the brake, it displays the normal "press start and brake to start engine" on the dash. When you do that, all of the IP and dash lights go dark, along with the radio if on. Only the dome lights remain (door open). The peanut lights remain on during this period. After around 5-7 seconds, it will revert back to ignition off with the ignition button glowing green. If I start by placing the ignition in 'run' before I press start, the same thing occurs when I press start, only after the 5-7 seconds it will revert back to 'run' with the IP illuminated and door chime, along with the battery icon and CEL illuminated (since the engine isn't running).

The next step is to grab my Tech2 when I have the next open day. Anyone have any thoughts as to why the PCM wouldn't be grounding the starter relay? Thanks!

 

[CWB]

Unplug, clean, Deoxit 5 and dielectric grease the PCM connector in question. While you have it apart, ground the wire coming from the starter relay to see if the motor spins (may not work if power comes from the PCM also through the same connector). May have to back probe the ground wire (connect to ground manually) while connector is connected to the PCM. Also Check the PCM ground itself. Good Luck

 

[V-SER1ES]

Unplug, clean, Deoxit 5 and dielectric grease the PCM connector in question. While you have it apart, ground the wire coming from the starter relay to see if the motor spins (may not work if power comes from the PCM also through the same connector). May have to back probe the ground wire (connect to ground manually) while connector is connected to the PCM. Also Check the PCM ground itself. Good Luck

If I’m understanding you correctly, you are talking about backprobe grounding the connector at the PCM that goes to the starter relay?

Is this expected to achieve a different result than manually switching the relay as I did, resulting in crank? I’m afraid I have lost you.

 

[CWB]

It just checks the wire between the relay and the PCM for any possible break. The unplug and replug may affect any corrosion at the connector. Good Luck

 

[strandediniowa50315]

What did you end up doing to get this resolved? I'm having the same problem. Push start and all goes black.

 

[V-SER1ES]

What did you end up doing to get this resolved? I'm having the same problem. Push start and all goes black.

Unfortunately I haven't found a resolution yet as I haven't had time to work on this project. However, I do have a Tech2 and found that there is no communication with the PCM, and a DTC for the TCM not receiving a signal from the PCM. So it appears that I may not be getting power to the PCM or the PCM may be bad? I am assuming that with CAN, the TCM could still talk to the PCM even if one of the wires were broken/high ohms. I have printed the diagrams for pinouts of the PCM and back probing them for power/grounds is my next step when I can get back to it.

 

[CWB]

V- Excellent troubleshooting technique. Wire repair is more likely and less expensive than module replacement. Good Luck
And thanks for keeping the forum informed.

 

[V-SER1ES]

Sorry for the delay and thanks for everyone's patience. I have had a chance to do some more diagnosis on this tonight, here are my findings:

I removed the covers from all three PCM connectors and used a back probing kit to get my Power Probe to the PCM inputs. I verified that at connector 1, there is 12v regardless of ignition position. At connectors 2 and 3, there is Ground regardless of ignition position. I also checked "Starter Relay Coil Control" (connector 1, pin 56) which should have 12v when ignition is in Run or Start, which it did, and reverted to Ground when ignition was off. Everything here seems normal.

I made a couple observations when attempting to start; mainly that when I placed the ignition in Run (holding the dash switch to "ACC" for a few seconds) I did not get the amber engine light on the dash that I expected (although maybe because the PCM isn't communicating with the IPC). There is also the amber Antitheft light that lights up constantly when in Run, and I don't know if that is typical or not. The fuel tank is also very nearly empty and the gauge is on E, but I don't expect that to cause any of these issues.

Is anyone aware if the Antitheft light stays on when in Run, on a car that is operating normally? Would Antitheft cause these sort of starting symptoms?

Thanks as always!

 

[Anoxias]

Sorry for the delay and thanks for everyone's patience. I have had a chance to do some more diagnosis on this tonight, here are my findings:

I removed the covers from all three PCM connectors and used a back probing kit to get my Power Probe to the PCM inputs. I verified that at connector 1, there is 12v regardless of ignition position. At connectors 2 and 3, there is Ground regardless of ignition position. I also checked "Starter Relay Coil Control" (connector 1, pin 56) which should have 12v when ignition is in Run or Start, which it did, and reverted to Ground when ignition was off. Everything here seems normal.

I made a couple observations when attempting to start; mainly that when I placed the ignition in Run (holding the dash switch to "ACC" for a few seconds) I did not get the amber engine light on the dash that I expected (although maybe because the PCM isn't communicating with the IPC). There is also the amber Antitheft light that lights up constantly when in Run, and I don't know if that is typical or not. The fuel tank is also very nearly empty and the gauge is on E, but I don't expect that to cause any of these issues.

Is anyone aware if the Antitheft light stays on when in Run, on a car that is operating normally? Would Antitheft cause these sort of starting symptoms?

Thanks as always!

Having the same problem with my 2009 4.6 as it sits next to my also broken 08 V lol I've replaced my ECM 3x, verified voltage at the relay, jumped terminals, starter works fine. Can you get a scan tool to connect? I can't even get that.
Guess I'm going to take one for the team and have a very expensive tow out of my garage, up the driveway and 40 miles to the dealership. I'll post findings here as this seems to have started being a more common problem.

 

[V-SER1ES]

Having the same problem with my 2009 4.6 as it sits next to my also broken 08 V lol I've replaced my ECM 3x, verified voltage at the relay, jumped terminals, starter works fine. Can you get a scan tool to connect? I can't even get that.
Guess I'm going to take one for the team and have a very expensive tow out of my garage, up the driveway and 40 miles to the dealership. I'll post findings here as this seems to have started being a more common problem.

No, my Tech2 will only read codes from the IPC, etc. Currently it shows the TCM and IPC both do not have communications with the ECM, yet my ECM seems to be receiving power/ground. I am starting to suspect that there is an internal relay built into the ECM that is not functioning properly.

Anoxias, I would be very grateful to hear what comes of yours, sorry to hear you are in the same pickle. I will still update this when I do some more diagnostics within the next few days.

 

[V-SER1ES]

Quick update and a question.

I did order some Deoxit D5, and I plan to use it on the ECM connectors shortly. I have also looked at a TSB from GM that cites terminal fretting at the transmission connector causing symptoms similar to what I am having, so I will be using it on that as well. I disassembled the underhood fuse panel to check for any broken/chewed wires underneath which contains the TCM) but everything was fit a a fiddle.

I am trying to stay focused on the issue here: the ECM isn't grounding the "POWERTRAIN RELAY CONTROL" circuit (highlighted in yellow in ECM diagram) which allows the relay to supply voltage to the coils/injectors/etc. This coupled with the fact that my MaxiSys and Tech2 will not communicate with the ECM, makes me think that it is an issue with a High Speed GMLAN data line.

My question is this: is anyone familiar with how the "ECM/TCM DATA WAKEUP" circuit works? (highlighted in yellow in the computer diagram) It appears this is a data line, although probing it shows 12V with key on/engine off. Could it be that the ECM just remains in sleep mode and is not getting the signal to wake up, or maybe that one of the other High Speed GMLAN (tan) wires have continuity issues and the ECM cannot communicate at all?

Anyway, thanks for reading along with me.

 

[V-SER1ES]

Alrighty folks, I finally got this figured out (I hope permanently).

I bought a pre-programmed PCM (spareecm on eBay out of Ohio - good phone support as well) and finally had the time to install it.

I followed the 30-minute security relearn process to get the codes between the RCDLR and the PCM, worked the first time. I used a spare battery hooked up with jumper cables to keep the voltage up during the process, and just barely stayed above 12.3V - even with every power-consuming device shut off that I could.

The car starts and idles good, but still need to complete CKP Variation Relearn. I cannot locate this special function on my Tech2, and when I attempted it on my Autel, the process stops at "start and idle engine."

Regardless, I hope this helps someone down the line. Thanks for your input!