Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Code B334 - Loss Of ECM Data: Notes
If BCM cannot exchange data with ECM and ignition is on, code B334 will be set. If other communication codes are stored along with code B334, see MULTIPLE INTERMITTENT CODES in this article. If code B334 is the only code stored, failure will be located as an open in circuit No. 800H, or an open in circuit Nos. 800J and 800G, or a faulty ECM or ECM MEM-CAL.
During a failure a fail soft value equal to 100°C will be used for coolant temperature. The cooling fans will be ran at high speed and no ECM diagnostic information will be available for display. While in the service diagnostic mode, this code will remain active, always checking for proper operation.
- Checks for intermittent operating conditions.
- Checks if open is in circuit No. 800H or rest of data circuitry.
- A double open condition is isolated in this step. Condition occurs on both sides of ECM, in dash side of data line.
- Isolates fault to be a poor terminal contact at engine dash harness interconnect circuit No. 800H or ECM.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.