B334 Loss of ECM Serial Data

Code B334 - Loss Of ECM Data:

Wiring Diagram for Codes B334, B335, B336 & B337:

CODE B334 - LOSS OF ECM DATA

Circuit Description:

Code B334 will set if the ignition is on and the BCM is not able to exchange data with the ECM. From the "Self Diagnostic System Check" we already know:

^ ECM is running and has power and ground
^ Data circuit is not shorted
^ Data is reaching the CRTC

This means the problem must be caused by an open circuit condition in the data circuit. There could be one open in CKT 800C or two opens in the data circuit, one on either side of 800C.

During the time the failure is present a substitute temperature reading for coolant will be used to allow continued operation of climate control. The cruise control and A/C clutch will be disabled. ECM service mode diagnostics and all output cycling will be disabled. The BCM will assume the engine is running if the key is on.



Test Description:

1. Checks for intermittent condition.

2. Checks to see if open circuit is due to open in engine side of CKT 800C or in rest of data circuit.

3. Since the fault could be caused by two opens in the data circuit (isolating the ECM), this step checks to see if there is anopen in CKT 800A. If circuit 800A is open, installing a permanent jumper between CKTS 800B and 800H will bypass both opens. If CKT 800A is not open, repairing the open in CKT 800B ofthe ALDL cover will bypass both opens, or repairing the open in the dash side of CKT 800C will fix the problem.

4. Checks to see if fault is due to poor terminal contact at engine to dash connector or the engine side of CKT 800C is open.



Note on Intermittents:

If only code B334 shows up as "History", check for momentary loss of ECM's ignition (CKT 439), battery (CKT 480), or grounds (CKTS 450A, 450X and 551). Reference chart A1.

If code B334 is set as "History", along with any of the following codes set as "History", B335, B336, B337, B552, B553, E047, see chart on "Multiple Intermittent Codes".

If code B334 is set as "history", along with code E051, follow code E051's respective chart.