Failed 'B' timing reference sensor (crankshaft or camshaft position sensor) due to internal open circuit or heat damage; Damaged or chafed wiring in the sensor harness, especially near hot exhaust components or sharp brackets; Corroded, loose, or backed-out pins at the sensor connector or ECM connector; Missing or damaged reluctor wheel teeth or a loose tone ring on the crank or cam sprocket; Excessive air gap between the sensor tip and the reluctor wheel caused by wear or incorrect installation; Electrical interference or a short to ground or power on the signal circuit; ECM internal fault on the timing reference input circuit, though this is less common

DTC codes / P03xx · Ignition system and misfire / P0379

P0379Timing Reference High Resolution Signal 'B' No Pulses

Q: What does code P0379 mean?

Timing Reference High Resolution Signal 'B' No Pulses. P0379 means the engine control module (ECM) is not receiving any pulses from the 'B' high-resolution timing reference signal, which is a secondary crank or cam position input used for precise fuel and ignition timing. The ECM has detected a complete loss of pulses on that circuit, so it cannot verify the exact rotational position of the engine from that source.

P0379 means the engine control module (ECM) is not receiving any pulses from the 'B' high-resolution timing reference signal, which is a secondary crank or cam position input used for precise fuel and ignition timing. The ECM has detected a complete loss of pulses on that circuit, so it cannot verify the exact rotational position of the engine from that source.

SystemPowertrain

Code typeGeneric (all makes)

SeverityMedium

Fix difficultyIntermediate

AreaIgnition system and misfire

Symptoms you may notice

Illumination of the check engine light, often with no other noticeable symptoms
Engine may crank but fail to start or start after a long crank
Rough running, misfiring, or stalling at idle or under load
Reduced engine power or limp mode due to lost timing reference
Intermittent no-start that may clear after the engine cools or wiring is disturbed

Common causes, most likely first

Failed 'B' timing reference sensor (crankshaft or camshaft position sensor) due to internal open circuit or heat damage
Damaged or chafed wiring in the sensor harness, especially near hot exhaust components or sharp brackets
Corroded, loose, or backed-out pins at the sensor connector or ECM connector
Missing or damaged reluctor wheel teeth or a loose tone ring on the crank or cam sprocket
Excessive air gap between the sensor tip and the reluctor wheel caused by wear or incorrect installation
Electrical interference or a short to ground or power on the signal circuit
ECM internal fault on the timing reference input circuit, though this is less common

How to diagnose and fix it

Scan all modules for stored and pending codes, then record freeze-frame data to confirm when P0379 sets
Visually inspect the 'B' sensor, its connector, and the reluctor wheel for physical damage, debris, or loose mounting
Measure sensor resistance and compare to the manufacturer's specification, then check for an open or short in the harness
Back-probe the signal wire at the ECM and crank the engine to look for a pulsed voltage or AC waveform with a multimeter or oscilloscope
Check for a short to ground or power on the signal circuit with the sensor disconnected and the key on
If wiring and sensor test good, substitute a known-good sensor and clear codes to see if the fault returns
If the code persists with a verified good sensor and wiring, perform a crankshaft variation learn or relearn procedure and inspect the ECM connectors before condemning the ECM

What the 'B' Signal Really Tells You

Many vehicles use the 'B' high-resolution signal as a backup or fine-timing input, so a failed sensor may not prevent the engine from running on the primary crank signal alone.
A common misdiagnosis is replacing the sensor when the real fault is a damaged reluctor wheel or a loose tone ring that has shifted and changed the air gap.
Heat and oil contamination can cause the sensor to fail only when hot, so a cold resistance check may pass while the code sets after the engine reaches operating temperature.
Aftermarket sensors with incorrect resistance or air-gap tolerances frequently set this code even when the original sensor was not the root cause.
A weak battery or poor engine ground can cause a no-pulse condition on the signal circuit, so always verify supply voltage and ground integrity before replacing parts.

Can I keep driving with P0379?

If the engine starts and runs without misfire or stalling, you can drive cautiously to a repair shop, but avoid heavy acceleration and long trips. If the engine cranks without starting or stalls repeatedly, stop driving and have the vehicle towed to prevent safety risk and further damage.

Tools that help

Tools we recommend are in the Auto Veteran shop on Amazon. As an Amazon Associate we earn from qualifying purchases.

Guidance is general and written for all OBD-II vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.