OBD-II trouble code
P0385: Crankshaft Position Sensor 'B' Circuit Malfunction
Your engine has two crankshaft position sensors, and the second one has a circuit fault. The first task is not testing the sensor — it is working out which of the two sensors on your engine is 'B'.
Quick facts
- System
- Powertrain
- Category
- Sensors / Timing
- Severity
- High severity
- Drivable
- No — stop driving until repaired
- Repair cost range
- $150 – $600
- DIY difficulty
- Intermediate DIY
What does P0385 mean?
P0385 announces something many owners never knew about their engine: it carries two crankshaft position sensors. The familiar codes — P0335 and its family — belong to sensor 'A'. This code and its four siblings (P0386 through P0389) belong to the second unit, and the powertrain control module has detected a fault in its circuit: no signal, an invalid level, or a signal it cannot reconcile with a turning engine.
Why fit two? The reasons vary by manufacturer, and knowing which applies to your engine predicts how the car will behave with the fault present. Some engines use the second sensor for redundancy — lose one and the other carries on, so the car runs normally and only the code betrays the problem. Some use it for faster starting: two pickups reading different wheels let the module establish exactly where the crank is within the first fraction of a revolution, so a 'B' failure shows up as longer cranking before the engine catches rather than as a running problem. And on some designs the two sensors read from opposite ends of the crankshaft — one at the front damper, one at the flywheel — partly because comparing them lets the module see torsional effects and misfires more precisely. The same code can therefore mean a car that drives perfectly, a car that starts lazily, or a car that stalls and strands, depending on which architecture you own.
That variety creates the practical trap with this code: location. Sensor 'A' and sensor 'B' are not standardised positions. On one engine 'B' is at the bellhousing reading the flywheel ring; on another it sits behind the crank pulley; on some diesels it is the pump-mounted pickup. Parts catalogues list both sensors, and ordering or replacing the wrong one is the most common way this diagnosis goes in circles. Identify 'B' from the service information for your exact engine before touching anything — it is ten minutes that regularly saves a wasted part and a repeat visit.
Once identified, the diagnosis itself is conventional crank-sensor work, with one free shortcut: the other sensor. If 'A' is reporting cleanly, the crankshaft is turning, its trigger wheel is intact, and any shared reference or ground is healthy. The fault then lives in what belongs to 'B' alone — its pickup, its private wiring run, or its connector — which is a short list on every engine.
Common causes
- Failed second crankshaft position sensor — heat, vibration and age affect it exactly as they do the primary
- Damaged or chafed wiring in the 'B' sensor's dedicated harness run
- Corroded, oil-soaked or backed-out terminal at the 'B' sensor connector
- Excessive air gap after the sensor was disturbed during clutch, transmission or timing work
- Metallic debris clinging to the magnetic tip and blunting the signal
- Damaged trigger wheel where the 'B' sensor reads its own separate wheel
- Poor sensor ground or shield connection allowing noise to swamp the signal
- Wrong replacement part fitted previously — the two sensors on one engine are often not interchangeable
Symptoms
- Check engine light with no other symptom at all on redundant designs
- Noticeably longer cranking before start-up, especially the first start of the day
- Hard starting or intermittent no-start where 'B' provides the start synchronisation
- Stalling or sudden cutting out on designs where the module needs both signals
- Misfire codes or rough running logged alongside, where the module uses the pair for misfire detection
- Tachometer flicker or dropout in some implementations
Diagnostic steps
- 1.Identify from service information which physical sensor is 'B' on this exact engine and where it mounts. Do not assume — positions differ even between engines from the same manufacturer.
- 2.Check whether any 'A' family codes (P0335-P0339) are stored alongside. Both families set together points to something shared: power, ground, or the module itself. 'B' alone points to the 'B' path.
- 3.Note the behaviour: normal running with a lit lamp, extended cranking, or stalling. The symptom identifies the architecture, and the architecture sets the urgency.
- 4.Inspect the 'B' sensor's connector and harness run first, particularly if clutch, transmission or front-end work was done recently — a disturbed sensor is a prime suspect.
- 5.Test the sensor per its type: winding resistance and AC output while cranking for a magnetic unit; supply, ground and square-wave switching for a Hall type.
- 6.Verify the air gap where it is adjustable or shim-set, and inspect the sensor tip for accumulated metallic debris.
- 7.If the sensor tests well, scope its signal at the module connector rather than at the sensor — a clean waveform leaving and a poor one arriving isolates the harness.
- 8.After replacement, complete any relearn procedure the platform requires; some modules must re-index the new signal before the code will stay away.
Repair cost
$150 – $600
The sensor itself is $30 to $150 for most applications. Fitted cost depends almost entirely on where 'B' lives on your engine: an accessible unit near the damper or on the block is $150 to $300 all in, while one buried at the bellhousing or behind engine mounts pushes toward $450 to $600 on labor alone. Wiring repairs fall in the same range as the accessible sensor. Before authorising work, confirm the quote is for the 'B' sensor specifically — the two sensors on one engine can carry very different labor times, and quotes based on the wrong one mislead in both directions.
Estimate your repair
Run the numbers for your vehicle
Open the Repair Cost Estimator with crankshaft position sensor replacement preselected. Adjust labor rate and vehicle category to fit your situation.
DIY vs shop
This is an intermediate DIY job. It usually involves diagnostic steps, specialty parts, and some careful work in tight spaces. If you have the tools and a service manual or trustworthy video for your specific vehicle, it is achievable in a weekend. Otherwise, a competent independent shop will be faster.