Truck problem:

This 2010 Chevrolet Silverado truck is losing power when put in reverse. Hooked up a scanner and instead of getting a transmission code we got this a p0326 for knock sensor performance code. It seems like the knock sensor is telling the engine to retard timing. Verified it with a scanner and yes it showed timing almost go below 10 degrees at idle. Changed the knock sensor but still the same. Reset engine code but no change. What would you recommend next?

ATS Adviser:

Looking at the knock sensor diagram, there are 2 knock sensors on this engine. Disconnect them both. The ecm is using them to detect to retard timing once the engine commands it. Compare timing degrees when connected and disconnected. When connected, rev up engine and watch timing. Should go up if normal. When disconnected, rev up again and timing should go up because signal of the tps sensor signal has increased. If no timing increase, check ECM for shorted power, ground and bus communication. In bus communication testing, disconnect the tcm since it is the one affected in reverse. You can bypass it using a jumper wire to the bus connection. If timing now goes up, transmission circuit is suspect. If power and ground supplies are within range for the TCM, replace the transmission.


You nailed it! When we disconnected the TCM module and jumpered it, the timing went up with the 2 knock sensors hooked up.

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