Diagnostic System Check - Engine Speed (VIN T, V)

Fig. 008 - WIRING DIAGRAM for DEC Engine Speed Check. VIN T, VIN V:

ENGINE SPEED CHECK

The ECM monitors engine RPM through the tach lead from the "R" terminal of the generator. Engine RPM is one of the inputs to the ECM to calculate the duty cycle of the EGR. With the key "ON", the "CHECK ENGINE" light will remain "ON" until the engine exceeds 400 RPM. If the tach signal is lost, the "CHECK ENGINE" light will remain "ON" after the engine exceeds 400 RPM.

Fig. 007 - Chart For DEC Engine Speed Check.:

1. Checks for V-ref. Should be about 5 volts. If V-ref. is lost due to a grounded wire or faulty ECM, the CEL will remain "ON" at any RPM.
2. Checks for grounded wire on ECM side of CEL bulb circuit. A grounded wire would keep CEL light "ON" with the engine running.
3. Checks tach signal output from generator. This is an A.C. signal, and should be over 7 volts A.C. at idle, and increase slightly with increased RPM. Since this is a generator output, if voltage is over 7 volts A.C., fault is not in generator or wiring up to the point of voltage measurement.