Feb. 09 2017
Feb. 09 2017

Vehicle: 2006 Chevrolet HHR, 2.2L 4 cylinder, VIN F, Automatic Transmission

Mileage: 111,846 miles

Problem: This vehicle came to the shop because the starter would stay engaged for 2-3 seconds after the engine started and the MIL was illuminated.

Details: The technician connected a scan tool and retrieved a DTC P0340, camshaft position sensor (CMP) circuit malfunction from the engine control module (ECM). There were no DTCs in the body control module (BCM). Looking at the parameter identification data, the technician noted that the ignition switch data was correct. At this point he called ALLDATA Tech-Assist.

The ALLDATA Tech-Assist consultant suggested that the tech scope-check the CMP signal from the ignition control module (ICM) to the ECM. NOTE: The starter relay is controlled by ECM and will crank the engine until it sees a correct RPM input signal.

In this case, the ECM was not correctly interpreting the rpm due to an erratic CMP signal from the ICM. NOTE: The ICM produces a 0-5volt square wave CMP signal. There is no physical CMP on this engine.

System Strategy: This ignition system does not use a conventional CMP that detects valve train position. The ICM identifies when the #1 or #3 cylinder has fired on the cylinder’s compression stroke using sensing circuitry integrated within each coil. The sensing circuit detects the polarity and the strength of the secondary voltage output. The higher output is always at the event cylinder. The ICM sends a CMP signal to the ECM based on the voltage difference between the event and waste cylinder firing energy. This system is called “compression sense ignition”. By monitoring the CMP and crankshaft position signals, the ECM can accurately sequence the fuel injectors. If the ECM does not receive a CMP signal from the ICM, a DTC P0340 will set.

Confirmed Repair: Because of the scope-pattern glitches the technician observed in the ICM’s CMP signal, he replaced the ICM and cleared the DTC. The problem was successfully repaired.

The ALLDATA Tech-Assist team fields cases like this every day. See how Tech-Assist can help your shop save time and money with on-call diagnostic support from ASE-certified Master Technicians. More Tech Tips 

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