B334

Code B334:

Loss Of Compass Module Circuit:

CIRCUIT DESCRIPTION:

Code B334 will set if the ignition is "ON" and the BCM is not able to exchange data with the ECM for 2.0 seconds. 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.
^ ECM MEM-CAL (PROM) is OK.

This means the problem must be caused by an open circuit condition, in the data circuit. Since the data circuit is a loop there must be two opens, one between the BCM and ECM pin 2A8, and the other between ECM to IPC. Only one circuit is needed for data circuit to function. During the time the failure is present, a substitute temperature reading for coolant (90°C) will be used, to allow continued operation of climate control. The cruise control and A/C clutch will be disabled. ECM service mode diagnostics will be disabled. The rear defog will be forced "OFF." The BCM will assume the engine is still in the same state as it saw before failure when it comes to engine running, WOT, and cumulative fuel.

TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.

1. Checks for intermittent condition.

2. Checks to see if open circuit is due to open in CKT 800F & BCM, or in rest of data circuit.

3. Checks to see if fault is in ECM or wiring.

4. Checks to see if fault is in BCM or wiring.

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 450, 450X). Reference CHART A1 under TESTING PROCEDURES. If code B334 is set as history, along with any other communication codes, see chart on MULTIPLE INTERMITTENT CODES. An improper or malfunctioning CAL-PAK could also cause this code to set.