Ignition Switch Communication Failure
The U1134 code indicates that the Powertrain Control Module (PCM) or Body Control Module (BCM/GEM) has detected invalid data or a complete lack of messages from the ignition switch over the SCP (J1850 VPW) communication bus. This prevents the modules from knowing the actual key position (OFF, ACC, RUN, START), affecting start authorization and power management.
1. Commonly Affected Makes
2. Most Common Causes
- Faulty ignition switch with worn internal contacts
- Open, short-to-ground, or short-to-battery in the ignition switch signal circuit to the BCM/GEM
- Internal failure of the BCM/GEM that processes the SCP signal
- Short, open, or incorrect termination on the SCP (J1850) bus
- Low battery voltage or poor ground connections on network modules
3. Symptoms You Will Notice
- Engine may not start or stalls unexpectedly
- No crank or no start condition
- Electrical accessories may not work properly
- Warning lights on the dashboard (e.g., security light)
4. Step-by-Step Diagnosis
Check battery voltage and ground connections at the BCM and PCM
Inspect the ignition switch wiring for opens, shorts, or damage
Test the ignition switch for proper operation in all key positions
Monitor SCP bus activity with a scan tool to verify communication
Check for other related codes (e.g., U1xxx) that may indicate bus issues
5. Frequently Asked Questions
Is it safe to drive?▼
No, this code indicates a high-severity issue that can cause the engine to stall or fail to start, potentially leaving you stranded. It is not safe to drive.
How much does it cost to fix?▼
Repair costs typically range from $150 to $600, depending on whether the ignition switch, wiring, or BCM needs replacement. Diagnostic fees are extra.