Powertrain
generic / SAE
P0642
Sensor Reference Voltage "A" Circuit Low
The 5 V reference voltage on the A circuit (used by multiple sensors) is below threshold — short to ground or excessive current draw by a single sensor pulling the rail down.
SystemPowertrain
Typegeneric / SAE
GroupP0
Range / number6 / 42
Possible causes
- Sensor or harness shorted to ground high
- ECU reference output damaged low
- Connector pins corroded - high contact resistance low
Symptoms
- Check engine light on
- Possible limp mode or no-start
- Multiple follow-up faults across modules
- Reset/relearn may be needed after repair
Inspection / repair
- Difficulty: hard
- DIY: shop recommended
- Estimated cost: 80–800 €
- Estimated time: 0.5–4 h
- Component: sensor reference circuit
- Component: ecu
- MIL / check engine light
- emissions-relevant
- limp mode possible
Sources
References
sae:J2012