P0340 on my mother's Aveo

[Ray Vanlandingham]

Hi.

My mom has a 2008 Chevy Aveo, purchased used from CarMax about a year and a half ago.. the car is in the 70-80k range. It is an LT, with the 1.6L engine.

Several months ago, she began having a check engine light. The code returned was P0340 (Camshaft Position Sensor 'A' Circuit Malfunction). Not having a o-scope to actually 'test' the output of the sensor with, and able to get one (OEM) for about $25 on Amazon, I replaced the sensor and wiped the code.

About a week later, another MIL. Checking showed not only the same P0340, but a P1346 (Intake Camshaft Position (CMP) Sensor System Performance). As it seemed that a possible cause at this point was a timing problem, I ordered a timing belt kit and dived in. Once disassembled, it was clear that the belt was a bit stretched... I was able to easily wiggle the belt, on the forward side, more than it's thickness, and thus move the crank pulley about half a tooth. It was clear from checking the marks that the timing belt had not skipped (and the engine has never indicated a miss) but I went ahead and put in a new timing belt, tensioner, and idler pulley. I did not replace the water pump, but did spin it to check... it's 'stiff' but does not grind, and I intended to pull this back apart at 100k and replace it. Again wiped the codes, drove the car a few miles, and no light. Yay, I thought.

About a week later, the P0340 returned (but not the P1346). When driving the car, she reports that after starting, and at the first few stoplights (when cold) the engine seems to 'lag' at giving power when the throttle is opened, but that once it's warmed up it seems to work fine.

I'm at a bit of a loss here, as I'm rather unsure what to do other than start playing the 'keep changing parts' game.... it seems possible that either the crank sensor is bad, or that it's some electrical or PCM issue.

-- Ray