Skip the auto shop - Our mechanics make house calls

P0378 OBD-II Trouble Code: Timing Reference High Resolution Signal B Intermittent/Erratic Pulses

Check Engine Light

P0378 code definition

If the PCM has stored the code P0378, it means that the system has detected an abnormal pulse reading from the high resolution timing reference signal B, which indicates that there is a fault with the system’s circuitry.

What the P0378 code means

Located in the injection pump is a sensor disk that emits pulses that the PCM uses to control fuel injection timing. The PCM tests for missed pulses, and compares those to the number of pulses it should be detecting according to the manufacturer. If this value is not correct or erratic, the PCM will store the code P0378.

What causes the P0378 code?

There are many things that could cause an erratic pulse reading between the sensor disk and the PCM. Most often, these include a defective crankshaft, camshaft, or distributor position sensors.

However, other causes may include:

  • Failure of the distributor
  • Open or shorted optical sensor
  • Faulty, corroded, damaged, open, or shorted wiring or connectors
  • Failed PCM, in rare cases

What are the symptoms of the P0378 code?

The P0378 code could be preceded by no symptoms at all besides the illumination of the Check Engine light. However, it could also be preceded by engine misfiring, knocking when accelerating, and decreased fuel economy.

How does a mechanic diagnose the P0378 code?

A mechanic should first abstract code information from the PCM with an OBD-II scanner, and check for other codes that may indicate a larger or related issue.

In order to diagnose the cause of the P0378 code, many mechanics begin by inspecting the crankshaft gear and crankshaft position sensor. This is accomplished by checking for the engine RPM signal while the engine is running. If there is no signal detected, then a visual inspection of the crankshaft and related components is necessary. The technician should repair or replace any components that are faulty. This process eliminates one of the most common issues for the P0378 code, and may help narrow the options for following repairs.

Common mistakes when diagnosing the P0378 code

When diagnosing the P0378 code, a common mistake is forgetting to clear the code and do a road test after performing each potential solution. This step should be done after each repair, to help narrow down the cause faster. By replicating the moment of failure, a mechanic may be able to discover the problem much faster.

Another common mistake with the P0378 code is automatically replacing the crankshaft, camshaft, or distributor sensors, rather than checking for mechanical distributor failure or other issues. Additionally, it is important to replace crankshaft or camshaft sensors as a set, rather than individually.

How serious is the P0378 code?

Because the P0378 code relates directly to how the PCM controls fuel injection and timing, this is a very serious issue that should be addressed immediately. Failure to address this issue when it is detected could result in the failure of other engine components when they aren’t able to obtain fuel, or correct fuel pressure.

What repairs can fix the P0378 code?

In order to address a P0378 code, there are a few repairs that a mechanic may choose to perform. These include:

In the rare case that the PCM is faulty, the mechanic may replace the PCM.

Need help with a P0378 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details
Icon-warranty_badge-02

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.

GET A QUOTE

More related articles

P0222 OBD-II Trouble Code: Throttle/Pedal Position Switch/Sensor B Circuit Low Input
P0222 code definition Throttle/Pedal Position Switch/Sensor B Circuit Low Input What the P0222 code means The manufacturer specifies a range of acceptable voltage to be produced from the throttle position...
How to Transfer a Car Title in Idaho
In order to prove ownership of a car, you must have the title. However, when a car is sold, given away or inherited, the title needs...
The Traveler’s Guide to Driving in Malaysia
CraigBurrows / Shutterstock.com Malaysia is a popular destination for many tourists today. The country has amazing sights and attractions that you will want to explore....


Related questions

Q: P1743

This code is for a transmission overdrive solenoid problem. The overdrive solenoid would need to be tested to see if it has the proper resistance of 10 to 20 ohms. If it is okay then the harness will need to...

Q: Why car won't start help. Tried to help with obd.

Among the possible faults that you have listed, the crankshaft position sensor (CPS) is particularly noteworthy. If the CPS has indeed failed such is a very common cause of no starts. Consequently, your most efficient option would be to request...

Q: Check Engine Diagnosis - Transmission controller Communication error codes

Hello there, many different faults can cause this combination of codes on your 2006 Chrysler PT Cruiser. When we see loss of communication codes with Transmission Control Module (TCM) internal faults, this usually means one of the following: ...