P0377

What it means

P0377 means the engine control unit has detected too few pulses from the high resolution timing reference signal on circuit B, which is a secondary crank or cam position signal used for precise timing. The control unit expected a certain number of pulses for the engine revolution and counted fewer than it should. How this signal is generated and which sensor is 'B' depends on the engine and model.

Symptoms

• Malfunction indicator lamp on
• Engine misfire or rough running
• Hard starting or long cranking
• Intermittent stalling or cutting out
• Loss of power or hesitation
• Engine runs in a limp or reduced performance mode

Possible causes

• Damaged or contaminated crankshaft or camshaft position sensor, or its reluctor/trigger wheel pickuplikely
• Wiring faults to the timing sensor: chafed, open circuit, short or high resistancelikely
• Poor connector contact, corrosion or water ingress at the sensor or control unit plugpossible
• Damaged, cracked, loose or debris-clogged trigger wheel or encoder ringpossible
• Incorrect mechanical timing, such as a stretched or slipped timing belt or chainpossible
• Electrical interference or low system voltage from a weak battery or poor earthspossible
• Faulty engine control unitrare

How to diagnose

1. Read all stored and pending codes and note freeze frame data, including engine speed, load and coolant temperature at the time of setting.
2. Check for related codes for crankshaft, camshaft or misfire faults, as these help to identify which sensor circuit is involved.
3. Visually inspect the timing sensor, its wiring and connectors for damage, oil contamination, corrosion and security.
4. Check battery condition and charging voltage, and inspect main earth connections.
5. With a suitable scan tool, compare live crank and cam signal status and engine speed readings during cranking and running.
6. Check the sensor signal and supply against the manufacturer's specification using an oscilloscope or multimeter, and wiggle-test the harness while watching for dropouts.
7. Inspect the trigger wheel for damage, missing teeth or debris, and check sensor air gap where adjustable.
8. Verify mechanical timing against the manufacturer's procedure if the signal checks are good or if the engine has had timing work.

How to fix

• Repair or replace damaged wiring and ensure connectors are clean, dry and fully seated.
• Replace the faulty timing reference sensor once the circuit has been proven good.
• Replace or correct a damaged or loose trigger wheel or encoder ring.
• Correct engine mechanical timing and replace worn timing components as required.
• Restore good battery condition and earth connections.
• Replace or repair the engine control unit only after all other causes are ruled out and the fault is confirmed.

Can I keep driving?

Nearby codes

• P0376GenericTiming Reference High Resolution Signal B Too Many Pulses
• P0378GenericTiming Reference High Resolution Signal B Intermittent/Erratic Pulses