Sensor Reference Voltage 'A' Circuit/Open
There's a problem with the reference voltage circuit for one of the sensors.
Heads up: this code wasn't in our hand-written library yet, so DiagCoach AI built this page on the fly. Double-check critical specs against service info before condemning parts.
What it means (plain English)
The engine's computer sends a steady voltage (usually 5 volts) to sensors to allow them to send data back. If that voltage isn't available, the computer cannot get readings, which triggers this code.
What the computer is actually seeing
The engine control module (ECM) detects a fault in the reference voltage circuit for one of the sensors on circuit 'A'. It typically sees a voltage lower than 4.5 volts or no voltage when it expects 5 volts.
What a healthy reading looks like
Reference voltage should be around 5 volts when the engine is running. A reading under 4.5 volts or no reading at all indicates a fault.
Guided diagnostic — the DiagCoach way
Don't just throw parts at it. Walk through these in order — each step tells you whether to keep going or stop and fix what you found.
- 1Check the wiring harness and connectors for any visible damage or corrosion. Repair if needed. Decision: Is damage found? (Yes: Repair it. No: proceed.)
- 2Using a multimeter, check the reference voltage at the connector for the sensor in question. Expected is around 5 volts. Decision: Is the voltage present? (Yes: Sensor may be faulty. No: Proceed.)
- 3Inspect the specific sensor and its alignment in the system. Replace the sensor if no voltage is found and wiring is intact.
Common causes
- Damaged wiring or connectors in the reference voltage circuit
- Failed sensors drawing too much power
- Short circuits to ground or positive
Typical repair cost
$$$
Related codes
Frequently asked questions
Is it safe to drive with P0659 active?
It's moderately severe, so drivability may be affected; fix soon but it's generally safe to drive short distances.
Can this code clear itself?
If the underlying problem is intermittent, the code may temporarily clear, but it will come back if the fault isn't fixed.
Why does this code appear with other sensor faults?
If multiple sensors share the same reference voltage circuit, a fault in that circuit can trigger multiple codes.
Working a real vehicle right now?
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