DTC 55

Fig. 064 - WIRING DIAGRAM for Code 55 5V Ref. Circuit. VIN N, VIN T:

CODE 55

5V REF. CIRCUIT

(INCORRECT VOLTAGE ON ECM TERMINAL "C")

4.3L VIN "T"

5.7L VIN "N"

The ECM regulates ignition supplied voltage from ECM terminal "A" down to 5 volts, which it supplies to the MAP sensor and Metering Valve Sensor (MVS) through ECM terminal "C". To aid in fault detection and diagnosis, a pull-up resistor is connected between "5V ref." terminal "C" and "MVS" terminal "R" inside the ECM. If the "MVS circuit from ECM terminal "R" is open, the voltage reading at terminal "R" will be about 5 volts.
Code 55 indicates that the ECM has seen either voltage too high or voltage too low at ECM terminal "C".

Fig. 063 - Chart For Code 55 5V Ref. Circuit.:

1. Checks ECM terminal "C" voltage with ignition on and engine stopped. Voltage should read 4 to 6 volts.
2. Determines if high voltage is result of short to B+ or faulty ECM.
3. Determines if low voltage is due to grounded circuit, MAP sensor, MVS or faulty ECM..
4. Since voltage reading in step #1 was normal, intermittent short or ground in ECM Terminal "C" circuits may be at fault.