2003 Cadillac CTS with high voltage on the 5 v reference line

CTS cranks but no start and the several codes showing high voltage on sensors (MAF, Camshaft position sensor (CMP), APP, ECT ). I did find the 5 lines going to the MAF were rubbing on the frame and shorting so I fixed them. I replaced the MAF, CMP and ECT sensors and replaced the MAF connector. I got some help for JustAnswers.com here www.google.com/url?sa=t&rct=j&q=&esrc=s&...qp9ckOu9QLdo6IEFR4hv

I also attached the scanner readout:



Can someone guide me on checking the computer grounds? The wiring diagram on JustAnswers.com is unclear on which lines are for the ECM ground. I verified that the ECM external ground is good by running current and showing a good ground.

Start with one code and check from there. If it were me, I'd start with something easy like the CMP sensor. Get some voltage readings on each of the wires while plugged in. You should have a 12v feed from the ECM fuse on the pink wire, ground from the PCM on the tan wire, and your signal on the brown and white wire. Make sure the power and ground will light a test light.

Unless you already have this fixed, measure those voltages and report back.

To answer your question, the main ECM ground is G100 located in the engine compartment, on the engine block near the starter motor. If you're missing a ground for the CMP sensor at the sensor, then check at the ECM. If it's missing at the ECM then check G100. That's the only ground I see for the ECM.

You'll want to make sure your block ground is good, too, since the ECM ground goes to the block. Check G102 on the inner fender wall near the battery and G105 on the engine block near the alternator.

I put the car on a lift, and used a video scope and could not find the ground near the starter. I'll check the other grounds you mentioned. I used a brake light and tested the CMP sensor and ECT and MAF sensors powers and grounds to the ECM connector C1. My problem is that with a new MAF sensor connected the common grounds for each of the sensors are about 8 volts with KOEO. Im thinking it's a ground problem. Thanks for the post and I'll do some tests tonight.

Interesting, the ground voltage elevates when the MAF is plugged in. Leave everything plugged in but leave the IMRC solenoid unplugged.

All the powertrain codes makes sense except for that IMRC code so my thinking is maybe the control wire for that solenoid is some how shorted to reference low?

Is there any continuity between the control wire of the IMRC solenoid and the reference low that goes to the CMP, MAF, ECT, stuff... ?

Is the intake manafold runner control selonoid at the top rear of the intake manifold? When I worked on the car I noticed it was unplugged so I plugged it in at the rear of the manifold. I'll unplug it and try the diagnostics again.

Ive got another problem now, the main relay seems to be out, as there is no power to the ECM or the Manifold fuses. The ECM is also not communicating with the scanner. I'll replace the main relay solenoid first.

Thanks so much for looking at this car issue. Your comments about the intake manifold runner control make sense. My problems seem to correlated with my plugging in that previously unplugged manifold runner control solenoid. I just thought it got unplugged accidently. Do you have the ability to check if there is a service repair writeup on this engine for the intake manifold control issue?

im having trouble with the key recognition, perhaps that's why the main relay and ECM fuse are not activated. Should I do the 30 min. relearn procedure for the key? Is there another way?

I don't know anything about this immobilizer system but no com to computer so check power and ground I guess. Gotta start somewhere.

When I made the suggestion to check for a IMRC control wire short to ground I might be incorrect assuming a short to voltage on the ground because I don't have enough evidence.

I neeed a loaded circuit voltage reading so when you get the MAF connected again and you have high voltage on the ground, does the TPS ground also show high voltage. I'm only picking on the TPS because I think it's easy to get to and it's on the other side of the ground tree in this diagram.
i.imgur.com/r1sQSb7.png

Hot at all times power at Pin 15, C2
i.imgur.com/X36XiCl.png

Im working on this now. I was able to locate the same car at the junk yard and I verified the wires and checked for continuity between the sensors we discussed. Thanks for your message and direction on troubleshooting this problem.

Im having trouble with the antitheft system, it dosn't recognize the key. My scanner has no communication with the ECM, and the main relay is not energized with KOEO. The scanner communicates and gives codes for other areas, just not the ECM. Is it normal for the main relay not to be energized with KOEO when the antitheft system is not recognizing the key? I tried the key relearn procedure ( 3 times cycle the key waiting 10 minutes with the key on between each cycle of on off) but there is apparently a large current drain when the key is on, because the battery quickly goes down below 12 volts. The current drain must be on a line not supplied by the main relay because the main relay is not energized now that the antitheft system is not recognizing the key. Should I check voltage drops across the powered fuses to find the high amp circuit?

Marti wrote:

no communication with the ECM, and the main relay is not energized with KOEO

Does the check engine light come on, do you have 5v reference at a 3 wire sensor? The ecm is needed in the antitheft circuit and must communicate. Check powers and grounds if computer's awol.

Also, are the other modules complaining of loss of communication with computer?

Marti wrote:

there is apparently a large current drain when the key is on, because the battery quickly goes down below 12 volts. The current drain must be on a line not supplied by the main relay because the main relay is not energized now that the antitheft system is not recognizing the key. Should I check voltage drops across the powered fuses to find the high amp circuit?

By all means please do. You did report of a relay getting hot so follow the heat and find out the source of the draw.

The "main relay mini" is not energized so there is no power to the ECM. I checked the mini relay with a tool for checking relays and I have a working main relay. I have a breakout box on this relay so I can measure the 4 leg volts. Here is a similar tool for relay testing that I use: www.amazon.com/Electronic-Specialties-19...83932699630276&psc=1

With KOEO the fuel pump does not run. I have a breakout box on the DLC and it shows battery volts, and 2 good grounds, the pin 2 (VPW+ PWM-) shows a blinking light that means communication. I get communication with other modules, just not the ECM. The chk engine light is not on, only the antitheft light. I was told that if the antitheft is activated, the ECM gets no power. Is that correct?

Eurika! The car is now recognizing the key and cranking. The underhood fusebox has a large connector called "eng w/h" that contains about twenty wires (lots of red ones with power) and connects into the fusebox. I disconnected it and reconnected it and Bingo. I had disconnected it recently and it apparently was not fully reconnected.

I used an ohm meter to check if the IMRC signal line had continuity with the common low reference (computer grounded line) that runs to (is common to) the MAF, CMP, and ECT. There is no continuity. Each of these sensors share the 12 volt power feed and there is continuity between these lines. I also found a donor car (2003 CTS with 3.2 liter) at the junk yard and found the same continuity with all the 12 v lines to these sensors. Also, that junk car had no continuity between the IMRC sensor line and the tan grounds to the other sensors. I'll send some pics tomorrow.

Marti wrote:

Each of these sensors share the 12 volt power feed and there is continuity between these lines. I also found a donor car (2003 CTS with 3.2 liter) at the junk yard and found the same continuity with all the 12 v lines to these sensors.

Do you mean the ground (low reference) has continuity ?
I don't think the ECT sensor has anything in common with the MAF or CMP, besides the shared ground (low reference).

I'm glad the immobilizer issue is sorted Now back to the main course lol. Plug in the MAF again and get the high voltage on the grounds again, and take a voltage reading at the TPS ground. You can unplug the TPS for this.

The TPS results as requested: with KOEO, unplugged 6 pins, the top end pins both about 5 v, the bottom 2 were both about 3.3 v, middle pins 10 and 28 mv. Tested voltage drops on fuses and the TCM/IPC fuse (10 A) had about 0.8 mv , The ECM/TCM fuse had the highest at 3 mv, and the only other with significant v drop was ign. switch fuse with 0.5 mv (other fuses near zero mv).

Is this the one you have 10 or 28 mV on? Tan wire?

If yes then this justifies taking a voltage reading on this wire at the computer. If the ground's good at the TPS, but bad at the MAF, then this is the area I'm most interested in:

If the voltage is low at pin 26 connector 1, but high at the MAF then it's time to start tugging on wires because it's looking like a bad wire or splice.