P06A8
Reference Voltage C Circuit Range/PerformanceP06A8 is a generic OBD-II powertrain diagnostic trouble code: Reference Voltage C Circuit Range/Performance. It is logged by the engine control unit when the powertrain monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P06A8 means
P06A8 is stored when the powertrain control module (PCM) detects that the reference voltage it supplies on the circuit designated "C" is out of its expected range. The module provides a stable reference voltage, most commonly five volts, to a group of sensors, and it continuously monitors that supply. When the measured voltage on reference circuit C drifts outside acceptable limits, the module records P06A8.
Depending on the manufacturer, the sensors fed by reference circuit C are frequently associated with the automatic transmission, transfer case, or one of the differentials, rather than the core engine sensors. Because several sensors can share one reference circuit, a fault here typically causes multiple sensor signals to read implausibly at the same time, so P06A8 is usually accompanied by more specific sensor range or performance codes.
The most common causes are a short to ground or short to another circuit on the reference wire, a failed sensor pulling the reference down, or wiring and connector damage. If P06A8 is stored entirely on its own with no companion sensor codes, an internal PCM fault or a control module programming error should be suspected. Diagnosis relies on a scan tool, a digital multimeter, and the manufacturer wiring diagram to isolate the affected circuit before replacing any parts.
Common causes
Most-frequently reported root causes when P06A8 is logged.
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1
Short to ground on the reference voltage "C" circuit wiring.
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2
Short to voltage or to an adjacent circuit on the reference "C" wire.
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3
A sensor on reference circuit C with an internal fault pulling the reference out of range.
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4
Chafed, pinched, or corroded harness wiring on the reference circuit.
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5
Corroded or loose connector at a sensor or at the control module.
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6
Failed internal reference voltage regulator inside the PCM.
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7
Control module programming or calibration error when the code is stored alone.
Symptoms drivers notice
How to diagnose P06A8
A typical diagnostic flow when this code is present.
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1
Retrieve all stored DTCs and freeze frame data, noting any companion sensor codes.
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2
Use the wiring diagram to identify which sensors are supplied by reference circuit C.
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3
Measure the reference voltage at the module and at the affected sensor connectors with a multimeter.
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4
Disconnect sensors on circuit C one at a time while watching the reference voltage to isolate a shorted sensor.
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5
Inspect the reference wiring and connectors along their length for chafing, shorts, corrosion, or damage.
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6
If the reference is out of range with all sensors disconnected but wiring is intact, suspect the PCM.
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7
Repair the fault, clear the codes, and verify all affected sensor readings return to normal.
Related powertrain codes
- P0600 — Serial Communication Link Malfunction
- P0601 — Internal Control Module Memory Check Sum Error
- P0602 — Control Module Programming Error
- P0603 — Internal Control Module Keep Alive Memory (KAM) Error
- P0604 — Internal Control Module Random Access Memory (RAM) Error
- P0605 — Internal Control Module Read Only Memory (ROM) Error
Frequently asked questions
What does the "C" in P06A8 refer to?
It is the manufacturer's label for one specific reference voltage circuit; different vehicles group different sensors on circuit C, so the wiring diagram is needed to know which sensors are affected.
Why do other sensor codes appear with P06A8?
Several sensors can share one reference supply, so if that supply goes out of range they all read incorrectly at once, producing companion range or performance codes.
Can P06A8 be caused by the PCM itself?
Yes. If the code is stored alone with no companion sensor faults, a failed internal reference regulator or a programming error in the module is a likely cause.
Is it safe to keep driving with P06A8?
It depends which sensors are affected; if a transmission or important control sensor loses its reference the vehicle may enter a default strategy, so it should be diagnosed promptly.
Disabling P06A8 in software
RaceTune can permanently disable P06A8 — and any other OBD-II diagnostic trouble code — on every ECU family we support. The monitor is disabled inside the ECU itself, so the fault stops being logged: the warning light stays off and the engine never enters limp mode for this code. The change is tied to your exact software version.
ECU families we can disable P06A8 on
We hold the DaVinci A2L disable definitions for these families, so the exact P06A8 path and mask addresses are mapped. verified marks a confirmed disable definition. We support many more — upload your file and our identifier will match it automatically.
- Bosch EDC17C66 verified
- Bosch EDC17CP57 verified
- Bosch MG1CP002 verified
Software modifications affect emissions compliance and are not road-legal in many jurisdictions. RaceTune service files are intended for motorsport, off-road, and export use.
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