P0FFF – Time Reference High Res Signal A Erratic Pulses

By Reinier (Contact Me)
Last Updated 2023-06-19
Automobile Repair Shop Owner

Table of Contents

1. What Does Code P0FFF Mean?
2. Where is the P0FFF sensor located?
3. What are the common causes of code P0FFF?
4. What are the symptoms of code P0FFF?
5. Get Help with P0FFF

What Does Code P0FFF Mean?

SPECIAL NOTES: Although OBD II trouble code P0FFF – “Time Reference High Res Signal A Erratic Pulses” is listed in two minor and largely incomplete online trouble code databases, code P0FFF is not listed in either the SAE J2012 standard or any of its revised versions, or the ISO 15031 standard or any of its revised versions.

As a practical matter, both the SAE J2012 and ISO 15031 standards list trouble code P0373- “Timing Reference High-Resolution Signal “A” Intermittent/Erratic Pulses” and as such, the origin of code P0FFF – “Time Reference High Res Signal A Erratic Pulses” is unclear. Nonetheless, since codes P0FFF and P0373 refer to exactly the same problem, code P0FFF likely originated in an automotive market that has not adopted either or both the SAE J2012 and ISO 15031 standards or have not made these standards legally binding on car manufacturers in that market.   

It is worth noting that because the above two standards are enshrined in law in both the US and most European and some Asian automotive markets, car manufacturers in these markets may only assign the generic trouble codes and their definitions that are contained in the SAE J2012 and ISO 15031 standards. END OF SPECIAL NOTES.

OBD II fault code P0FFF (or P0373, depending on the source consulted) is a generic code that is defined as, “P0FFF – “Time Reference High Res Signal A Erratic Pulses”, and is set when the PCM (Powertrain Control Module) detects erratic ignition trigger signals from the crankshaft position sensor.

The ignition systems on all modern vehicles work in the same way, in the sense that a crankshaft position sensor generates ignition trigger signals in conjunction with a toothed reluctor wheel that is mounted on the crankshaft. As the reluctor wheel rotates, the teeth on the wheel create electrical signals that the PCM uses as signals to create ignition sparks, as well as for misfire detection purposes.

In all cases, reluctor wheels incorporate a reference point in the form of a “missing” tooth, which is referenced to the position of piston #1. This reference point creates a signal that differs from the regular signals the crankshaft position generates, and this different signal is the starting point from which the PCM calculates all ignition strategies and initiates several complicated processes that allow an engine to start.

As a result, all engines (except most modern engines with STOP & GO functionality) start on cylinder #1, and in fully functional ignition systems, all ignition trigger signals will be generated at fixed intervals, since the teeth on the reluctor wheel are spaced at equal distances apart.

However, all of the above assumes that the teeth on the reluctor wheel are a) all present and undamaged, or b) that the correct reluctor wheel for a specific application is present on an affected vehicle. In the first case, damaged, missing, or clogged teeth could cause the crankshaft position sensor not to generate consecutive signals, which the PCM will interpret as erratic signals since the signals are not generated at equal intervals.

In the second case, an incorrect reluctor wheel might generate regular and consecutive signals, but at times when the PCM does not expect to see ignition trigger signals, which circumstance the PCM will also interpret as erratic signals, because the signals are not referenced to the known starting point in any engine cycle*.

* Regardless of the number of cylinders an engine has, an engine cycle is equal to two full engine revolutions, i.e., 720 degrees of crankshaft rotation, since each of the four engine strokes takes 180 degrees of crankshaft rotation to complete.

Regardless of the cause(s) of erratic ignition trigger signals though, when such signals do occur, the PCM will recognize that it cannot control the ignition timing, or calculate appropriate ignition timing strategies to suit changing engine operating conditions effectively, and it will set code P0FFF (or code P0373, depending on the source consulted), as a result. In some cases, the PCM might also illuminate a warning light on the first failure, but in most cases, the failure must occur multiple times before the PCM will illuminate a warning light.

Where is the P0FFF sensor located?

This image shows the location of a crankshaft position sensor relative to the teeth on a reluctor wheel, which forms an integral part of the harmonic balancer (aka crankshaft pulley) that fits on the front end of the crankshaft on most modern engines. Note that in some engines, the reluctor is located inside the engine where it forms an integral part of the crankshaft, and in these cases, the crankshaft position sensor is located on the outside of the engine’s crankcase

In this image, the small yellow arrow indicates the air gap between the sensor tip and the teeth that must be within a prescribed range if the sensor is to work optimally. Since the magnetic field that crankshaft sensors generate is typically very small, an air gap that is too large could cause the sensor to not work at all, while an air gap that is too small could potentially damage the sensor and the reluctor wheel.

Note, though that damaged reluctor wheels are not individually replaceable. If the reluctor wheel on an affected vehicle must be replaced, the entire harmonic balancer (aka the crankshaft pulley) must be replaced.

What are the common causes of code P0FFF?

Some common causes of code P0FFF (or P0373, depending on the source consulted) could include one or more of the following-

• An accumulation of mud, dirt, and/or snow between the teeth on the ring could, and often does, reach the point where the distance between two or more teeth is plugged with dirt. If this happens, the mud/dirt/snow effectively bridges the gap(s) between the reluctor wheel’s teeth, which makes it impossible for the sensor to detect individual teeth on the reluctor wheel
• Broken, damaged, or missing teeth on the reluctor wheel: such damage could result from impact damage with road debris, or careless handling of the harmonic balancer during transport, storage, installation (on the engine), or removal (from the engine)
• Using an incorrect or unsuitable harmonic balancer. Although any two given harmonic balancers may appear to be identical in all respects, the replacement unit may have more or fewer teeth than the original, or the spacing between the teeth may be different from the original

NOTE: Differences between the number of teeth and the spacing between teeth, on reluctor wheels are not always easy to spot with a casual inspection. Therefore, we strongly recommend that you do not source this critical part from online retailers that offer parts for suspiciously low prices because you can never be sure that are getting the right part for your specific vehicle. Bear in mind that the number of teeth and the spacing between them, as well as the profile of the teeth and the position of the ignition reference point on reluctor wheels, are critical factors that underpin the efficient operation of all gasoline engines.

What are the symptoms of code P0FFF?

Common symptoms of code P0FFF (or P0373, depending on the source consulted) could include one or more of the following but note that a) not all of the symptoms listed here will always be present on all affected vehicles, and b) the intensity of some of the symptoms listed here may vary between different vehicle makes and models-

• Stored trouble code and possibly an illuminated warning light
• Depending on both the application and the nature of the problem, multiple additional codes may also be present, with codes relating to misfires being the most common additional codes
• An enforced no-start condition may be present that will persist until the fault is found and corrected
• If the engine does start, it may run roughly, the idling quality may be poor, and/or the engine may not run at idling speed at all
• The engine may misfire severely at some or all engine speeds and loads
• Varying degrees of power loss may be present
• If the engine does start and run even passably well, the engine’s fuel consumption may increase dramatically
• The engine may stall unexpectedly or repeatedly at low to moderate engine speeds
• The engine may overheat severely even under light, or no-load conditions
• Severe engine knocking may occur at some, or all engine speeds and loads
• Catalytic converter damage or failure may occur on some older vehicles
• Some readiness monitors may not initiate or run to completion
• The vehicle will not pass a mandatory emissions test

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