P0378 Code Meaning and Next Steps

First checks take 10 minutes for basic checks. No special tools are usually needed for the first checks.

Can you keep driving?

Stop driving if any of these apply

!The check-engine light is flashing or the engine is shaking badly.
!The vehicle is stalling, struggling to accelerate, or obviously running rough.

If the light is steady and the vehicle still drives normally: Maybe, but only for a very short distance if the engine still runs smoothly.

What to check first

Step-by-step checks

1
Free - no tools
Check whether the engine runs rough, stalls, or has starting trouble at the same time
2
Free - no tools
Inspect the timing sensor connector and harness for looseness or heat damage
3
Basic tool needed
Look for metal debris near the sensor or signs of a damaged target wheel
4
Basic tool needed
If scan data is available, compare reference signal behavior with engine RPM while the fault occurs
5
Basic tool needed
Check whether the code appeared after timing work or sensor replacement

If the code returns

-If the signal drops when the harness is moved, wiring or connector repair becomes more likely.
-If the signal is unstable only when hot, heat-related sensor failure moves up the list.
-If the code returns after connector repair, recheck sensor gap and mounting.

Background

What this code means

P0378 is a generic OBD-II code for an intermittent or erratic high-resolution timing reference signal.

That usually means the controller is losing confidence in the timing pattern. Heat, vibration, or contamination can make the signal come and go.

Diagnosis

Common causes

Most common

Loose timing sensor connector

A loose connector can make the signal drop in and out.

Common

Wiring damage or corrosion

Heat, vibration, or contamination can make the signal erratic.

Common

Failing timing sensor

The sensor may work some of the time and then drop out.

Possible

Damaged target wheel

A distorted reference pattern can look intermittent to the controller.

Avoid these mistakes

What not to do

xDo not replace the ECU first if the sensor or target wheel is visibly damaged.
xDo not ignore intermittent stalling or no-start symptoms that line up with the code.

Parts

Parts that may need replacing

PartTypical costNotes

Timing sensor$40-$180Worth checking when the pulse pattern drops out intermittently.

Connector or wiring repair$50-$250Useful when the signal is loose, contaminated, or intermittent.

Target wheel or reluctor repair$200-$900Relevant when the reference pattern is mechanically damaged.

Related OBD codes

P0376

P0376 means the engine timing reference high-resolution signal has too many pulses.

P0377

P0377 means the engine timing reference high-resolution signal has too few pulses.

P0379

P0379 means the engine timing reference high-resolution signal has no pulses.

Source notes

Generic OBD-II (SAE J1979 / ISO 15031-5). P0378 was seeded from dtcdb and then expanded around intermittent timing reference faults, with emphasis on sensor, wiring, and target-wheel checks.

This guide is written as a generic multi-make reference, so bulletin history, sensor locations, and repair order can still change by manufacturer and engine family.

This is generic OBD-II guidance and should not override vehicle-specific service information. Exact diagnosis and repair steps vary by make, engine family, and model year.

Last reviewed: 2026-04-10

Reference: Open reference

P0378 - The Engine Timing Reference High-resolution Signal Is Intermittent or Erratic