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Showing results for tags 'odd combination of codes'.
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Throwing this one out to the masses. I had an opportunity to diagnose a 1999 996 C2 (not my own) which has some very odd symptoms. The car is idling somewhat rough, but not alarmingly so, and there is a slight pop (not quite a backfire) from bank 1 exhaust (psgnr side pipe). That is pretty much the only unusual noise, aside from some slight "pinging" noise coming from bank 2. The owner reports its down on power throughout the range. I scanned the stored codes (no CEL) and found the following: p1531 Camshaft adjustment, bank 1 P0341 Camshaft Position Sensor 1 - Signal Implausible, Short to Ground, Short to B+ p1340 Timing chain out of position, bank 1, Below lower limit or above upper limit Ok, probably bad actuator right! So I looked at the cam deviation, both very steady. Bank 1 25 degrees Bank 2 3 degrees Everything makes sense so far, the actuator is stuck "open" or in the relaxed advanced intake cam position (which is 25 degrees TDC by design). Here's where it gets very very strange. I cleared the codes, and then ran the engine again, at idle and 3000 rpm. I actuated variocam on bank 1 manually with Durametric at warm idle the engine responded as I am used to for this test with a wildly fluctuating idle and a whoooshing noise. Bank 2 behaved the same way. Head scratching time. Re-read the codes: p1340 Timing chain out of position, bank 1, Below lower limit or above upper limit P0341 Camshaft Position Sensor 1 - Signal Implausible, Short to Ground, Short to B+ ?????? How could this be, actuator seems to be working in both banks, 25 degrees in bank 1 (stable), AND a p1340 ???? So I rotated the engine to TDC, and pulled the green caps to look at the exhaust timing slots. Bank 2 was straight up. Bank 1 EXHAUST appeared to be about 12 degrees advanced at the cam (25 deg at the crank). What is strange to me is that variocam advances the intake cam only since the exhaust cam is fixed to the IMS tube with the drive chain. If an actuator fails, I can't surmise a reason why an actuator failure would cause an exhaust cam to advance by 25 degrees TDC. So in other words, variocam appears to be working correctly in bank 1, but that bank has somehow managed to advance itself (both intake and exhaust) to 25 degrees. Although the P0341 might indicate that we can't rely on the intake cam position and need to check the allocation manually. I halfway want to just re-time the engine and see what happens, but the other half of me suspects doom and gloom, unfortunately, and I guess with wild speculation until the cam covers are pulled, a huge variety of possibilities. Cam sprocket was fine but then somehow slipped after 3000 miles on the car since internal engine work Cam to cam chain slipped, jumped several teeth Exhaust cam to IMS tube jumped several teeth Guide rail, tension, or cam pad problem (too much slack?) IMS tube bank 1 sprocket slipped Seizure in valve train forced exhaust cam sprocket to slip exactly 25 degrees (coincidence that variocam advance is also 25 degrees?)