2001 C5 4.2 (AWN) Grounding Issue

[Beebster]

Some background first.

Car was throwing P0342 - Camshaft Position Sensor Bank 1 circuit low. I did a quick check of the wiring harness and voltages (12v and 5v) were both good, as was ground. Figuring it was the sensor I ordered a OEM Bosch sensor and installed. Still threw P0342.

After a little more digging is appeared the charging system might be the culprit if diodes were going/gone and RFI was running rampant. I had the charging system checked and the first place could not check due to "noise" which would back up the RFI possibility. I took it to another shop, with better diagnostic equipment and verified that loaded the alternator was only putting out 12.7v so I ordered a Bosh Reman unit. Installed it. Getting good voltage now but still have the same P0342 code.

Decided to check wiring/connectors again. This time I unplugged the bank 1 sensor and checked everything with the car running. Previously with the ignition in the "on" position I read zero resistance to ground on the connector pin. With the car running I get 35-50 Ohms resistance. I also get .055v on the ground pin of the connector, where there was zero with the ignition in the "ON" position.

The Bentley manual shows the ground as '220- Ground connection (sensor ground), in engine compartment wiring harness'.

Anyone have an idea where that wiring harness ground is located?

Thanks in advance.

[Beebster]

Car has been parked for a while, just getting back to this issue. Any ideas.....anyone...….Bueller?

[S/RConcepts]

There are 3 places that come in mind to check.

The first one is the most obvious, but check the grounds on the driver's side shock tower... its a bunch of brown wires clustered together. I've seen quite a few times where the insulation has flaked off of various ones and the wire strands are green and fuzzy.

The second place is less obvious, and that's the single ground wire located on the rear of the passenger's side cylinder head, just above the EGR (combi) valve. It should be a brown wire with a yellow stripe, and of thin gauge.

The third place is the ground wire located on the engine block behind the alternator. You've mentioned the alternator was replaced recently, but I'm wondering if perhaps the ground wire has worked itself loose or corroded over time. It's a thick gauge wire that's also part of the alternator/starter harness.

Best of luck in tracking this problem down!

[Beebster]

S / RConcepts thanks for the reply.

I have actually checked all of the above mentioned grounds as well as the one on the back of the firewall. Removed, cleaned and tested all of them, all check good. Through the checking I determined that the "220" ground is in fact one of the brown wires on the firewall. I also have a headlight aiming warning light that seems tied to the same problem. They worked fine until this issue came up, and now the aiming does not function and I get a warning light. I've checked each plug and sensor and both seem to be OK.

One thing I had not considered previously is that the transmission was rebuilt at the same general time as this problem occurred (maybe exactly, don't remember). Instead of rebuilding my transmission they rebuilt a transmission they had on the shelf and DID NOT install a rebuilt valve body. It has never shifted correctly since the rebuild. I have bought a ZF reman valve body to install, just haven't done it. Is it possible that something internal to the vavle body, like solenoids, have a shorting issue? Would this show up on the same ground circuit as the sensors? This is exactly why I HATE letting other people work on my cars.

[S/RConcepts]

I suppose that IS possible, however very unlikely... it'd be the first time I've seen such an issue, that's for sure! If you have VAG-COM or OBDEleven, check for TCM faults, they may point to a wiring issue.

More likely is whomever installed the transmission didn't install a ground properly, or pinched one somewhere. The transmission wiring itself is very simple, the bulk of it being contained in the harness plug on the driver's side front of the transmission right by the pan. You do have to remove the starter in order to change the trans, of course, and that's where the large ground located behind the alternator would come into play, but if you've checked that one already (and you're certain it's OK) this one can be ruled out. Also, make sure to confirm that the battery ground is clean and tight.

Let me look over some of the wiring schematics I have to see if I can come up with anything more, but I can't recall more grounds than the ones I previously mentioned.