P0389
Crankshaft Position Sensor B Circuit IntermittentP0389 is a generic OBD-II powertrain diagnostic trouble code: Crankshaft Position Sensor B Circuit Intermittent. 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 P0389 means
P0389 is stored when the Powertrain Control Module (PCM) detects an intermittent or erratic signal from the secondary crankshaft position sensor — designated "Sensor B" — typically a second reluctor-ring sensor used on engines with dual CKP arrangements or crankshaft-mounted tone wheels at both ends of the crank. Unlike a flat-out signal loss (P0386/P0388), the intermittent nature of P0389 means the circuit functions correctly most of the time but suffers momentary dropout caused by micro-fractures in wiring, loose connector pins, or internal sensor coil degradation.
The PCM relies on continuous crankshaft position data to schedule fuel injection and ignition timing. Even brief signal interruptions cause the PCM to momentarily cut fuel or retard spark, producing stalling, hesitation, or RPM dips. Because the fault is intermittent, it may not be present during a static inspection and can prove elusive to reproduce on a lift. An oscilloscope is usually required to catch transient signal drops, and a harness wiggle test while monitoring live waveform data is the most reliable method to isolate chafed insulation or cracked solder joints. A healthy Sensor B output typically reads 0.5–1.0 V AC at 300–600 Hz; intermittent drops to 0 V confirm the dropout.
Common causes
Most-frequently reported root causes when P0389 is logged.
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1
Micro-fractured or chafed crankshaft position sensor B wiring harness (flex fatigue near routing clamps)
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2
Corroded, spread, or loose sensor B connector pins
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3
Internal CKP sensor B coil wear or contamination causing voltage fluctuation
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4
Oil or coolant contamination wicking into the connector and degrading insulation resistance
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5
PCM Sensor B input-circuit solder crack or moisture intrusion in the amplifier channel
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6
Damaged reluctor ring (missing or bent teeth generating intermittent missing-tooth events)
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7
Excessive crankshaft end-play causing sensor-to-ring air-gap variation
Symptoms drivers notice
How to diagnose P0389
A typical diagnostic flow when this code is present.
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1
Connect a scan tool, retrieve freeze-frame data, and record live Sensor B frequency and voltage during idle and a road test
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2
Perform a harness wiggle test while observing the Sensor B signal on an oscilloscope — intermittent drops to 0 V confirm wiring or connector failure
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3
Visually inspect the sensor B harness for cracked insulation, heat damage, chafing against brackets, and corrosion at the connector
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4
Check wiring continuity with a DVOM (expected 0.5–2 Ω); test for short-to-ground and short-to-power on the signal wire
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5
With the connector disconnected, measure sensor B coil resistance (typically 200–900 Ω per manufacturer spec) and compare against spec
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6
Inspect the reluctor ring for missing, bent, or corroded teeth that could cause random signal gaps
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7
If wiring and sensor pass all tests, test the PCM B-channel input pin with a known-good signal source before condemning the module
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
Why does the stall happen randomly and not every time I drive?
The intermittent nature of P0389 means the dropout only occurs under specific conditions — typically vibration, temperature expansion, or mechanical stress on a partially broken wire or loose pin. The fault may seal itself when cold or stationary, which is why oscilloscope testing under load is more reliable than a static resistance check.
Can I drive safely with P0389 active?
Short trips at low risk are generally tolerable, but an intermittent CKP stall at highway speed or during a turn is a genuine safety hazard. The code should be addressed promptly; avoid high-speed driving until repaired.
Is P0389 the same as P0336 or P0385?
No. P0336 covers CKP Sensor A range/performance, and P0385 covers CKP Sensor B circuit presence. P0389 specifically flags the B circuit as intermittent — the signal exists but drops out unpredictably, which points to wiring or connector issues rather than a completely dead sensor.
Will replacing the sensor always fix P0389?
Not always. Because the root cause is most often a harness micro-fracture or corroded connector rather than the sensor itself, replacing the sensor without inspecting the wiring frequently fails to resolve the fault. Oscilloscope waveform analysis and a wiggle test are essential before condemning the sensor.
Disabling P0389 in software
RaceTune can permanently disable P0389 — 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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