Sensor Reference Voltage "A" Circuit Open
The 5 V reference voltage that the ECU supplies to multiple sensors (TPS, MAP, accelerator pedal, etc.) has dropped out or is open-circuit. Symptoms cascade — many sensor codes appear at once, all related to the same reference rail.
Affected components
- Ecm
- Sensor reference wiring
Common causes
- High likelihood: Reference wire shorted to ground (one defective sensor pulls the rail down)
- Medium likelihood: ECM internal reference output failed
- Low likelihood: Pin pushed back out of connector body
Possible symptoms
- Check engine light on
- Possible limp mode or no-start
- Multiple follow-up faults across modules
- Reset/relearn may be needed after repair
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
- Reduced-power or limp mode may occur
Sources
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.