OBD-II Code
P0387
Severity
Not yet reviewed
Nobody on our side has assessed this code yet, so we are not going to guess at how serious it is.
Can you drive it
We cannot say
Treat it as unknown until a shop reads it with live data. If the check-engine light is FLASHING, stop driving as soon as it is safe to — that means an active misfire, whatever the code.
Indicative cost (USD)
$130–$550
From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
P0387 means the CKP-B signal is reading LOW — either signal voltage is below the controller's lower threshold (typically under 0.3 V on a Hall-effect output that should swing 0-5 V, or under 0.3 V AC peak on a VR sensor at cranking when it should produce 0.5-1.5 V AC), or the signal-return circuit is shorted to ground.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then follow the diagnostic notes further down this page, in the order they are written.
They are written in the order a shop works this code, cheapest checks first. Where they name a component, inspect its wiring and connector before replacing it.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Check engine light
Read the full diagnostic procedureP0387 means the CKP-B signal is reading LOW — either signal voltage is below the controller's lower threshold (typically under 0.3 V on a Hall-effect…
P0387 means the CKP-B signal is reading LOW — either signal voltage is below the controller's lower threshold (typically under 0.3 V on a Hall-effect output that should swing 0-5 V, or under 0.3 V AC peak on a VR sensor at cranking when it should produce 0.5-1.5 V AC), or the signal-return circuit is shorted to ground.
Cheapest-first ladder
- key-on, backprobe the CKP-B signal wire at the sensor connector and read voltage with the DMM — a Hall sensor sits high (5 V) or low (0 V) at rest depending on the reluctor tooth position, and a wire stuck at 0 V key-on regardless of crank position confirms a short-to-ground in the signal lead or a dead sensor pulling its output low.
- Disconnect the sensor and re-measure at the harness side — if the harness pin now reads the expected 5 V supply, the sensor was internally shorted and is the fault; if it still reads 0 V, the wiring is shorted or the PCM-side supply is dead.
- Crank-test with a scope and verify pulse amplitude: a healthy Hall CKP-B shows clean 0-5 V transitions at 300+ pulses/sec at 200 rpm cranking; a VR sensor shows 0.5-1.5 V AC at cranking and grows to 5-15 V peak-to-peak by 2,500 rpm — amplitude under 0.3 V at cranking on a VR sensor confirms a weak/dead coil or excessive air gap.
- Inspect the connector pins for corrosion and verify the shield drain wire is grounded on shielded-cable applications. Expensive-misdiagnosis caveat: before replacing the CKP-B, check the air gap and reluctor — an air gap above spec (over 1.5 mm on most applications) reads as low signal amplitude on a VR sensor and trips P0387; the sensor and harness are fine, but the mounting boss has been damaged or the shim is missing.
Vehicle-specific patterns2002-2014 Subaru EJ-series throws P0387 from a chronic mounting-boss crack on the secondary sensor that lets the sensor sit too far from the reluctor…
- 2002-2014Subaru EJ-series throws P0387 from a chronic mounting-boss crack on the secondary sensor that lets the sensor sit too far from the reluctor, dropping VR amplitude below threshold.
- 2004-2013Subaru turbo (WRX/STI) throws P0387 acutely from the same root cause exacerbated by heat.
- 2003-2010Ford 6.0L Powerstroke throws P0387 from a chafed signal wire near the front cover that shorts intermittently to the cover itself.
- 2001-2010GM Duramax LB7-LMM throws P0387 from corroded sensor-connector pins where the harness routes near the steering knuckle and sees salt spray.
- 2004-2011Mazda RX-8 secondary back-up sensor throws P0387 from oil contamination at the tip.
Estimated repair$130 to $550.
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