2003 Cadillac CTS PO343, cam sensor high voltage.

This Cadillac CTS came in with PO343 Cam sensor high voltage

Initially we were going to replace cam sensor. Removed an watched for camshaft lobe to turn and it does. But voltage remains at battery voltage even with engine cranking over. Found cam sensor was receiving battery voltage on the low Reference and the signal wire

When ecm was disconnected the short to voltage goes away. We got replacement ecm and it did same thing. As you can see on picture. The short to voltage on signal wire remains at battery voltage even with sensor unplugged

If you disconnect ecm there are no shorts to voltage on that wire. Only with ecm connected

Have unplugged all sensors to ecm thinking maybe one sensor short was back feeding and short to voltage remains on signal wire and low reference wire too

Any ideas would help. With voltage staying high on signal wire. We have no square wave signal obviously from cam sensor. Diagram attached. And live lab scope voltage at cam sensor signal wire. Hope someone has seen this before. Maybe Someone here can shine some light on this. Need a break

Not on this vehicle. 12 Volts comes on pink wire from Ecm fuse. Signal wire should show square wave form not constant voltage. You may be thinking of another vehicle. But on this 2003 CTS. There is low reference for
pcm , signal which is where the square wave comes back to pcm and the voltage feed directly from fuse

It’s okay appreciate you anyway. Hopefully someone here can shine light. I will say pcm is a reman from gm. But who knows

Monde is right. The signal wire is either a pull up or pull down. Low reference is gm name for a computer ground to a sensor. Does test light light when connected to battery positive and probing low reference terminal? It should withkey on

Yes this is a pull down. Type. But it remains at battery voltage no matter what we do even with engine cranking. Battery voltage is on pink wire. And pull down on signs wire. But it should not remain at battery voltage without square wave signal.

Signal wire doesn’t receive voltage from pcm. It only sends back square wave from 0 to battery voltage square wave signal back to pcm. Voltage is supplied by Fuse on pink wire. Low reference is like you said pcm ground which in this instance is always showing battery voltage on that wire too. Have checked for short to voltage on both reference and signal with pcm unplugged and no short to voltage. Only when pcm is connected does it show voltage again on both signal and low reference

0 voltage with pcm disconnected on both low reference and signal. I’m almost certain it s a bad pcm

The CMP has three wires... 12v power, 5v signal, and a ground. The 12v is constant from the ECM fuse, the signal gets its 5v from the ECM at pin 8 and the ground is shared with the ECT and MAF at splice S111 and connects to the ECM via the C1 connector at pin 26. If you check, you're probably getting 12v on the ECT and MAF ground and signal wires as well.

Your square wave should be 5v - 0v on the CMP signal wire. As you noted, the 12v power wire has shorted to the ground wire. With the CMP unplugged, KOEO, you should have 12, 5, and 0 at the CMP connector (harness side). If you don't, unplug the C1 connector at the ECM and check pin 8 for the 5v ref and pin 26 for ground. Seems, 03 CTS's have this problem... either trace and locate the pinched wire/s or run a new one's. Remember, the ground is shared with the MAF and ECT so where ever the short is, it affects all three sensors.

Let me double check all of this. Definitely need to find the short. I do show battery voltage on the low reference/ground. I’ll find it in am

Check under the air filter box... MAF wiring loom gets crushed and cut by metal frame in that area. MAF shares it's ground with the CMP and ECT.

Going back to vehicle with your input VegasJak. With pcm connected we have battery voltage on both signal and low reference circuits. Unplugged coolant temp sender no change, but when disconnected the mass air flow reference voltage dropped to 0. This may have been what took out the pcm.

However, even with mass air disconnect I’m still showing battery voltage on cam signal wire Brown/White wire. Disconnected pcm connector. And checked voltage at Pin 8 and it always shows battery voltage.

Only way voltage drops complete is but pulling power from pcm

Unfortunately it may need pcm after all. Any additional thoughts before we give it time or death?

Yep. Looked into possible places where chaffing may have caused and loom looks clean. Will check for short on harness anyway. But short goes away with mass air flow sensor disconnected. I would assume if short was in harness the short would remain even with mass air flow disconnected right?

ECM's are pretty hardy and don't blow easily. I would check the following pins for voltages at the ECM with the C1 connector disconnected KOEO. Pin 8, 10, 24, 40, 56, 57, 58.
Check pins 26, 42, 51, 59, 62 as good grounds.
If the wiring problem caused the ECM failure and you don't correct that first you may end up blowing the replacement ECM.

No voltage at any of those pins except pin26, 9.9 volts appears when you plug in mass airflow sensor. If you unplug mass airflow sensor voltage disappears. See attached picture. Voltage at pin 3 of mass airflow which is shared low ref with cam and ect sensor. Voltage remains at 9.9.

So add a redundant ground wire. Backprobe the low ref add jumper to battery negative.

Forget the power probe. Use regular incandescent test light connected to battery positive. Probe low ref does it light with key on???

I added ground directly to battery ground on low ref. It brings voltage down but still nothing out of pcm. I believe we have lost it

Does the power feed on the pink wire light test light

What is it your looking for out of the pcm? Keep ground on low ref plug sensor back in and backprobe signal wire while cranking

Stupid question have you checked another cam sensor on the other bank to compare readings to plugged in and unplugged.