What Does P0400 Mean?
The crankshaft position sensor B circuit is sending an intermittent signal to the ECM. On engines that use dual crankshaft sensors or a secondary crank sensor for redundancy, this code indicates the backup or secondary sensor has an unreliable connection. The driver may experience intermittent stalling, random misfires, or momentary engine cutouts that may not be easily reproducible.
Common Causes
35%
Damaged or corroded wiring/connector at the secondary crankshaft position sensor
30%
Failing crankshaft position sensor B with heat-sensitive intermittent fault
15%
Crankshaft reluctor wheel with minor damage or debris accumulation
12%
Excessive crankshaft endplay causing variable sensor air gap
8%
ECM ground circuit issue causing intermittent signal interpretation errors
Diagnostic Steps
1
Monitor crankshaft position sensor B signal live data while the engine is running — look for signal dropouts or RPM spikes/dips that indicate intermittent signal loss.
2
Perform a thorough wiggle test of the sensor connector, harness, and ECM connector while watching the signal — reproduce the fault if possible.
3
Measure sensor resistance (typical: 500–1,500 ohms depending on type) cold and hot — compare to sensor A. An intermittent sensor often shows resistance changes when heated with a heat gun.
4
Inspect the sensor mounting and air gap to the reluctor — verify proper installation torque and gap specification (typically 0.5–1.5mm).
5
Check all engine and ECM ground straps for tightness and corrosion — a poor ground can cause erratic sensor readings system-wide.
Estimated Repair Cost
$80 - $350
Parts + labor, varies by vehicle and location
The crankshaft position sensor B circuit is sending an intermittent signal to the ECM. On engines that use dual crankshaft sensors or a secondary crank sensor for redundancy, this code indicates the backup or secondary sensor has an unreliable connection. The driver may experience intermittent stall...
The most common cause of P0400 (Crankshaft Position Sensor B Circuit Intermittent) is: Damaged or corroded wiring/connector at the secondary crankshaft position sensor
Typical repair costs for P0400 range from $80 to $350, depending on the vehicle, location, and whether you do it yourself or go to a shop.
An intermittent crank sensor can cause the engine to stall without warning, including at highway speeds. This is a safety concern. Limit driving and have the vehicle diagnosed as soon as possible. If stalling occurs, pull over safely and have the vehicle towed.
Start by connecting an OBD2 scanner to read the code and any freeze frame data. Then follow the diagnostic steps specific to P0400 to identify the root cause.
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Quick Info
Category
Powertrain
System
Engine Timing / Ignition System
Difficulty
Type
Generic (SAE)
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