What Does P0385 Mean?
The ECM has detected a general malfunction in the crankshaft position sensor B circuit. This secondary CKP sensor (sensor B) is used on some engines alongside the primary sensor A for redundancy or for additional timing precision. A circuit malfunction means the ECM is receiving no signal, an out-of-range signal, or a signal that does not correlate with sensor A. The engine may run rough, misfire, have degraded performance, or fail to start if the ECM requires both sensors.
Safety Warning
Loss of CKP sensor B can cause engine stalling if the ECM cannot compensate with sensor A alone. On engines that require both sensors, the vehicle may not start. Have the vehicle diagnosed promptly. If the engine runs, drive directly to a repair facility; avoid highway driving due to stalling risk.
Common Causes
35%
Failed crankshaft position sensor B (open circuit, shorted, or degraded output)
30%
Damaged, corroded, or disconnected wiring or connector in the CKP B circuit
15%
Contaminated or damaged reluctor ring associated with sensor B
10%
Incorrect sensor air gap causing no or weak signal generation
10%
ECM internal failure on the CKP B input circuit
Diagnostic Steps
1
Verify CKP sensor B has no signal by monitoring live data. Check the RPM PID from sensor B (if available separately) while cranking. A 0 RPM reading from sensor B with normal reading from sensor A confirms the B circuit is faulty.
2
Disconnect the CKP sensor B connector and measure sensor resistance. For magnetic (VR) sensors, expect 500-1500 ohms between signal pins. For Hall-effect sensors, verify 5V reference and ground are present at the harness connector.
3
Check for voltage output from the sensor while cranking. A magnetic sensor should produce at least 0.3V AC; a Hall-effect sensor should produce clean 0-5V square waves. No output with correct resistance indicates a reluctor ring issue.
4
Inspect the CKP B wiring from sensor to ECM for damage, paying close attention to routing near hot exhaust components, moving parts, and sharp edges. Verify no shorts to ground or power on signal wires.
5
Verify the reluctor ring is intact and properly positioned. Check the sensor mounting bolt torque and sensor air gap. Some sensors use a built-in spacer that wears off on first installation — ensure the gap is within specification.
Estimated Repair Cost
$80 - $450
Parts + labor, varies by vehicle and location
The ECM has detected a general malfunction in the crankshaft position sensor B circuit. This secondary CKP sensor (sensor B) is used on some engines alongside the primary sensor A for redundancy or for additional timing precision. A circuit malfunction means the ECM is receiving no signal, an out-of...
The most common cause of P0385 (Crankshaft Position Sensor B Circuit Malfunction) is: Failed crankshaft position sensor B (open circuit, shorted, or degraded output)
Typical repair costs for P0385 range from $80 to $450, depending on the vehicle, location, and whether you do it yourself or go to a shop.
Loss of CKP sensor B can cause engine stalling if the ECM cannot compensate with sensor A alone. On engines that require both sensors, the vehicle may not start. Have the vehicle diagnosed promptly. If the engine runs, drive directly to a repair facility; avoid highway driving due to stalling risk.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0385 to identify the root cause.
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Quick Info
Category
Powertrain
System
Ignition / Engine Timing System
Difficulty
Type
Generic (SAE)
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