P0377 OBD-II Trouble Code: Timing Reference High Resolution Signal B Too Few Pulses

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Cost of diagnosing the P0377 code

P0377 is a diagnostic trouble code (DTC) for "Timing Reference High Resolution Signal B Too Few Pulses". This can happen for multiple reasons and a mechanic needs to diagnose the specific cause for this code to be triggered in your situation. Our certified mobile mechanics can come to your home or office to perform the Check Engine Light diagnostic. Once we are able to diagnose the problem, you will be provided with an upfront quote for the recommended fix and receive $20.00 off as a credit towards the repair. All our repairs are backed by our 12-month / 12,000-mile warranty.

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P0256 code definition

Trouble code P0256 is defined as timing reference high resolution signal B too few pulses.

What the P0256 code means

In short, this code gets logged by the PCM (Powertrain Control Module) when it has noticed an irregularity present in the high resolution timing reference signal. The “signal B” element of the code is a reference to where in the system circuitry the problem is occurring and not necessarily identifying a specific component that’s being affected.

There is a predetermined range of degrees of deviation from the standard that the PCM will tolerate from the high resolution engine timing signal. The range is different across all makes and models and even amongst different engine sizes/types. When the timing signal is registered as outside of this range, the P0277 code is stored.

What causes the P0256 code?

The most common reason for this code being logged is because the crankshaft, camshaft and distributor positions sensors have all become defective. However, if that’s not the case, the second most likely reason is mechanical distributor failure. This is especially likely in the case of rear-wheel drive domestic vehicles with high mileages.

When it’s neither of these two reasons, the culprit is probably going to be wiring that has become corroded, faulty or is otherwise damaged. Problems with the electrical connectors could be to blame too.

Finally, if nothing else, the PCM could be the issue if it’s not taking readings correctly, but this is a long shot.

What are the symptoms of the P0256 code?

Often the symptoms associated with the P0256 code will be completely undetectable. On the other hand, they can be quite serious too and include things:

  • Spark knock upon acceleration
  • The engine misfiring
  • Poor fuel economy

The Check Engine Light is usually a symptom, but not all the time. With some vehicles, the PCM will actually wait until the problem is detected multiple times before this light is activated. Between that and the possibility of a complete lack of noticeable symptoms, the problem associated with P0277 can persist for a long time before it gets addressed.

How does a mechanic diagnose the P0256 code?

A mechanic will begin the diagnosis process with their OBD-II scanner to make sure they know all the codes that have been stored. They’ll then go and check on the crankshaft, camshaft and distributor sensors. The wiring and connectors will also need to be examined to see if they need to be replaced, repaired or cleaned.

Common mistakes when diagnosing the P0256 code

Although the camshaft, crankshaft and distributor sensors can be the source behind the P0256 code, a full diagnosis needs to be carried out before these important components are replaced. Far too often, a mechanic will simply replace these items the moment they see the P0277 code come up on their OBD-II scanner.

If a sensor needs to be replaced, it’s usually a good idea to change out both of them to avoid future problems. OEM sensors are best to use.

How serious is the P0256 code?

The owner isn’t at risk of death by driving a vehicle with this code logged, but it’s never a good idea to keep using an automobile when it runs the risk of misfiring. Aside from the obvious, the longer the problem persists, the higher the likelihood that the engine will need to be replaced which will definitely be expensive.

What repairs can fix the P0256 code?

The most common ways to fix the P0256 code include:

  • Changing out the camshaft, crankshaft and distributor sensors
  • Replacing, repairing or sometimes just cleaning wiring and electrical connectors
  • In rare circumstances, the PCM may need to be replaced

Additional comments for consideration regarding the P0256 code

The P0277 code is a tough one because, first, it can easily go unnoticed and, secondly, fixing it can mean little more than cleaning some wires or it can mean carrying out major replacements.

Need help with a P0277 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 1-800-701-6220.

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