P0393
Camshaft Position Sensor B Circuit High (Bank 2)P0393 is a generic OBD-II powertrain diagnostic trouble code: Camshaft Position Sensor B Circuit High (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 P0393 means
P0393 is stored when the PCM detects a signal voltage from the exhaust Camshaft Position Sensor B on Bank 2 that is persistently above the expected maximum threshold. In a typical Hall-effect CMP sensor circuit, the signal wire toggles between near 0 V (low) and near the 5 V reference (high) as camshaft reluctor teeth pass the sensor. A "circuit high" fault means the signal wire is stuck at or near supply voltage rather than toggling, which prevents the PCM from reading cam position transitions.
The most common cause is an open circuit in the signal return path — a broken signal wire, a pulled-back connector terminal, or a disconnected sensor — which allows the PCM's internal pull-up resistor to hold the line at 5 V. A short-to-voltage on the signal wire from a chafed harness contacting an ignition-voltage source produces the same result. Engine oil leaks onto connectors can also cause pin corrosion that effectively opens the signal path. Without Bank 2 exhaust cam data, the PCM disables VVT on that bank and uses a fixed injection and ignition strategy, reducing power and fuel efficiency. Diagnosis follows the same circuit-isolation logic as P0392 but focuses on open-circuit and short-to-power conditions rather than shorts to ground.
Common causes
Most-frequently reported root causes when P0393 is logged.
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1
Open circuit on the CMP Sensor B signal wire (broken conductor, pulled terminal, damaged connector)
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2
Short-to-battery or short-to-ignition voltage on the signal wire pulling it to supply level
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3
Disconnected or improperly seated sensor connector allowing PCM pull-up to dominate the line
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4
Corroded or oil-fouled connector pin creating an open-circuit condition
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5
Failed CMP sensor with open internal circuit (Hall-effect element failure)
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6
Blown fuse in the sensor supply circuit leaving the signal floating near B+ through leakage
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7
PCM internal pull-up circuit fault holding signal high (rare, confirmed only after ruling out wiring)
Symptoms drivers notice
How to diagnose P0393
A typical diagnostic flow when this code is present.
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1
Retrieve DTCs and freeze-frame; confirm P0393 is current and note any companion CMP or VVT codes that might indicate a broader circuit fault
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2
With ignition on (engine off) and sensor connector disconnected, measure signal wire voltage at the harness side — voltage at or near 5 V is normal (PCM pull-up); voltage above 5 V (near battery) indicates a short-to-power in the harness
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3
Reconnect the sensor and measure signal voltage again — if signal remains stuck high with a known-good sensor, the wiring has an open between sensor and PCM
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4
Perform a continuity test on the signal wire from sensor connector to PCM pin; an open reading confirms a broken conductor or pulled terminal
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5
Inspect the harness routing near the Bank 2 exhaust manifold for melted or chafed insulation that could create a short-to-power on the signal wire
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6
Check the sensor connector for oil contamination, spread or corroded pins, or improper seating; clean and reseat before replacing the sensor
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7
If all wiring checks pass, substitute a known-good CMP sensor and retest; if fault persists, test PCM signal input per OEM procedure
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
How is P0393 different from P0392?
P0392 means the signal line is stuck low (near 0 V), pointing to shorts-to-ground or a shorted sensor. P0393 means the signal line is stuck high (near 5 V or supply voltage), which typically indicates an open circuit in the signal path or a short-to-power. The repair strategy is opposite: P0392 — look for shorts to ground; P0393 — look for opens or shorts to voltage.
Is P0393 more serious than P0390?
Both codes disable Bank 2 exhaust CMP feedback with similar drivability consequences. P0393 and P0390 are equally urgent — neither is safe to ignore long-term because continued operation without cam timing data degrades efficiency, risks catalytic converter damage, and may eventually cause a no-start.
Can heat damage to the exhaust side harness cause P0393?
Yes, and it is one of the most common causes. The Bank 2 exhaust CMP sensor is physically close to the exhaust manifold. Heat can melt wire insulation, creating a short-to-power against any nearby hot-side circuit, which drives the signal line high and sets P0393.
Will clearing the code and driving fix it?
No. P0393 will return immediately or within a short drive cycle if the underlying open or short-to-power condition is still present. Clearing the code is useful for confirming a repair was successful, but it does not address the fault.
Disabling P0393 in software
RaceTune can permanently disable P0393 — 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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