Code B334, Loss Of ECM Serial Data (Riviera): Notes

Fig 1: Code B334 Flowchart, Loss of ECM Serial Data (Riviera)

Fig 2: Code B334, Loss of ECM Serial Data (Riviera)

Fig 3: Code B334 Schematic, Loss of ECM Serial Data (Riviera)

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, and 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 circuit 800C, or 2 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 ignition key is on.

1. Checks for intermittent condition.
2. Checks to see if open circuit is due to open in engine side of circuit 800C or in rest of data circuit.
3. Since the fault could be caused by 2 opens in the data circuit (isolating the ECM), this step checks to see if there is an open in circuit 800A. If circuit 800A is open, installing a permanent jumper between circuits 800B and 800H will by-pass both opens. If circuit 800A is not open, repairing the open in circuit 800B or the ALCL cover will by-pass both opens, or repairing the open in the dash side of circuit 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 circuit 800C is open.