P0392
Camshaft Position Sensor B Circuit Low (Bank 2)P0392 is a generic OBD-II powertrain diagnostic trouble code: Camshaft Position Sensor B Circuit Low (Bank 2). It is logged by the engine control unit when the ckp/cmp monitor detects that a specific fault threshold has been exceeded — typically resulting in the malfunction-indicator lamp (MIL / check-engine light) being illuminated.
What P0392 means
P0392 is triggered when the PCM measures a signal voltage from the exhaust Camshaft Position Sensor B on Bank 2 that is continuously or persistently below the minimum threshold. The sensor circuit operates with a 5-volt reference supply, a ground return, and a signal wire; when the signal pin reads at or near 0 V with the engine running, the PCM interprets this as a circuit low condition and stores P0392.
The most frequent electrical cause is a short-to-ground on the signal wire — oil contamination, chafed insulation against a grounded chassis point, or a connector pin touching the sensor body can all pull the signal low. A completely dead sensor that outputs nothing (open internal circuit) can also produce a low-voltage reading. Less commonly, a failed PCM input transistor that sinks the signal to ground is responsible. Without cam timing feedback, the PCM disables active VVT control on Bank 2 and may enter a reduced-power strategy. Catalyst overheating is a secondary risk if enrichment occurs during the fallback mode. Diagnosis prioritises isolating whether the short is in the wiring, the sensor itself, or the PCM before parts are replaced.
Common causes
Most-frequently reported root causes when P0392 is logged.
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1
Short-to-ground on the CMP Sensor B signal wire (chafed insulation touching chassis or engine block)
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2
Oil contamination inside the sensor connector shorting the signal pin to ground
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3
Failed CMP sensor with internally shorted or open signal coil outputting zero volts
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4
Broken signal wire with the cut end resting against a grounded surface
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5
Corrosion or moisture bridging signal and ground pins inside the connector
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6
Low battery or charging system voltage dropping the reference supply below sensor operating range
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7
PCM input-channel transistor failure sinking the signal line to ground (rare)
Symptoms drivers notice
How to diagnose P0392
A typical diagnostic flow when this code is present.
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1
Scan for all DTCs and freeze-frame; confirm whether the low voltage is present at idle or only under specific conditions
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2
With ignition on (engine off), measure the signal wire voltage at the sensor connector — below 0.2 V with the sensor disconnected confirms a short-to-ground in the harness
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3
Visually inspect the Bank 2 exhaust CMP sensor harness for chafed or melted insulation, especially near exhaust manifolds and routing clamps
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4
Check for oil contamination inside the connector; clean with electrical contact cleaner and re-test before replacing sensor
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5
Test sensor resistance (coil-type) or perform a bench power test (Hall-effect type) per manufacturer specification to confirm sensor integrity
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6
Use an oscilloscope to look for waveform presence — a flat 0 V line confirms no signal output; a low-amplitude noisy signal suggests a failing sensor rather than a wiring short
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7
If wiring and sensor both test good, test the PCM signal input pin resistance to ground (should not be near 0 Ω); consult OEM service data before condemning the PCM
Related powertrain codes
- P000A — A Camshaft Position Slow Response Bank 1
- P000B — B Camshaft Position Slow Response Bank 1
- P000C — A Camshaft Position Slow Response Bank 2
- P000D — B Camshaft Position Slow Response Bank 2
- P0010 — A Camshaft Position Actuator Circuit (Bank 1)
- P0011 — A Camshaft Position - Timing Over-Advanced or System Performance (Bank 1)
Frequently asked questions
What is the difference between P0392 and P0390?
P0390 is a general circuit code set when the PCM detects any malfunction on the Bank 2 exhaust CMP circuit. P0392 specifically identifies the failure mode as a low-voltage condition, which helps narrow the diagnosis toward shorts-to-ground, dead sensors, or broken wires rather than open circuits or intermittent faults.
Can a bad ground cause P0392?
Paradoxically, a poor sensor ground can sometimes cause P0392 if the ground reference floats and the signal pin reads incorrectly low relative to the PCM ground. Always verify both the 5 V reference and the ground circuit at the sensor connector before replacing the sensor.
My battery was replaced recently — could that cause P0392?
A weak battery or charging system fault that drops reference voltage can disrupt sensor operation and store circuit codes. Perform a battery load test and verify alternator output (13.5–14.5 V) before pursuing sensor or wiring repairs.
Will the engine start at all with P0392?
Usually yes, but with difficulty. The PCM can start the engine on crankshaft position data alone and fall back to a batch or paired injection strategy, but sequential fuel delivery and VVT control are compromised, causing extended cranking and rough running.
Disabling P0392 in software
RaceTune can permanently disable P0392 — 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.
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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