DTC 55

Trouble Code Chart 55:

Wiring Diagram - Code 55:

CODE 55


Circuit Description:

Code 55 says that the ECM has seen one of the following:

^ Grounded 5V reference (Terminal "21")

^ High voltage on the O2 sensor circuit

^ High voltage in ECM

Test Description:

1. Checks to see if fault is in the O2 sensor circuits if the light remains "OFF" or in the 5V ref. circuits if the light came back "ON".

2. This step checks for proper 5V reference.

2A. Determines if the source of high voltage is the ECM, or the wire harness shorted to 12V, by disconnecting the harness from the ECM.

2B. Determines if the source of low voltage is a ground in circuit to Term. "21" of the ECM or the ECM itself


2C. Determines whether source of fault is in O2 sensor circuits or ground in 5V reference circuit. A normal circuit should read under 1 volt (.3-.45 volts).


3. Checks for source of high voltage on O2 circuit by separating harness from ECM. If voltage remains high, fault is not in ECM.


4. Voltage under 1 volt is normal. This step checks for intermittent ground in 5V reference circuits.