OBD-II Code
P0388
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)
$140–$600
From this code's diagnostic notes. Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
P0388 means the CKP-B signal is reading HIGH — signal voltage is above the controller's upper threshold (typically above 4.8 V on a Hall-effect output, or above 15 V peak on a VR sensor that should max at 5-15 V peak-to-peak at 2,500 rpm), or the signal wire is shorted to the 5 V reference or to battery voltage.
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 procedureP0388 means the CKP-B signal is reading HIGH — signal voltage is above the controller's upper threshold (typically above 4.8 V on a Hall-effect outpu…
P0388 means the CKP-B signal is reading HIGH — signal voltage is above the controller's upper threshold (typically above 4.8 V on a Hall-effect output, or above 15 V peak on a VR sensor that should max at 5-15 V peak-to-peak at 2,500 rpm), or the signal wire is shorted to the 5 V reference or to battery voltage.
Cheapest-first ladder
- key-on, backprobe the CKP-B signal wire and read voltage with the DMM — a Hall sensor stuck at 5 V regardless of crank position confirms either an internal sensor failure or a short to the 5 V reference.
- Disconnect the sensor connector and re-read at the harness — if the harness pin now reads 5 V with the sensor disconnected, the wire is shorted to the reference inside the harness; if it reads the expected open-circuit value, the sensor is internally failed.
- Scope the signal at cranking — a healthy Hall CKP-B swings 0-5 V cleanly, and a VR sensor produces 0.5-1.5 V AC at cranking, rising to 5-15 V peak-to-peak by 2,500 rpm. A VR output above 18 V peak indicates a shorted-turn condition or a short to a higher-voltage line.
- Check for water intrusion at the sensor connector — moisture between the signal and 12 V pins bridges the two and reports as 'high circuit voltage.' Expensive-misdiagnosis caveat: before replacing the CKP-B sensor, verify the 5 V reference at the PCM-side connector is the correct 5.0 V (+/- 0.1 V) — a failing PCM reference regulator that's outputting 7-9 V will cause every Hall-style sensor on that reference bus to read as 'high circuit'; replacing one sensor won't fix the problem and the next sensor will set the same code.
Vehicle-specific patterns2002-2014 Subaru EJ-series throws P0388 from a known harness rub-through near the alternator bracket that shorts the secondary CKP signal wire to the…
- 2002-2014Subaru EJ-series throws P0388 from a known harness rub-through near the alternator bracket that shorts the secondary CKP signal wire to the 12 V alternator output line.
- 2004-2011Mazda RX-8 throws P0388 from internal sensor failure on the secondary rotor-position back-up sensor — the tip soaks oil over time and the internal Hall element shorts.
- 2007-2014RAM Cummins 6.7L throws P0388 from water intrusion at the CKP connector behind the starter, where the connector boot degrades and lets moisture in.
- 2008-2013BMW N57 inline-6 diesel throws P0388 from a known sensor failure where the Bosch unit's internal output transistor shorts to the supply rail.
Estimated repair$140 to $600.
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