Car problem question:

2003 Nissan Altima has intermittent no starts in the morning. When scanned for code, there is P0340 cam sensor fault code. As per common fixes, this code is set if the cam sensor is missing or the timing chain is stretched. The timing chain was checked OK and we are thinking of just buying a new cam sensor so we fix it once and for all. Do you have any suggestion?

ATS Adviser:

Looking at the cam and crank wiring connections to the ECM, these 2 sensors share an common vref supply shown in the red wirings, a common blue ground wire and a 3rd blue gray signal wire. Actually, the engine will run with the cam sensor disconnected except it will have a long cranking time during start ups.

You can measure the vref voltage during cranking and expect to get 5 volts from ECM. If not, replace the ECM. However, if the vref signal voltage is present, replace the cam sensor. Try using an OEM sensor since the aftermarket ones have a lot of problems.

Shown below is an approximate 5 volt VREF diagram for this vehicle's sensors:

2003 Nissan Altima Vref Wirings

For more details, you can get an exact wiring diagram for this vehicle from most parts store when you buy parts or get it FREE online 24/7 when you join ATS.


You got it right! We got the 5 v signal at KOEO at the ECM terminal. However, there was none at the cam sensor wire itself. The terminal connection was loose and corroded. Putting a new cam sensor and fixing the wiring corrected the problem.

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