P0321 – Crankshaft position (CKP) sensor/engine speed (RPM) sensor range/performance problem

By Reinier (Contact Me)
Last Updated 2018-02-21
Automobile Repair Shop Owner

Table of Contents

1. What Does Code P0321 Mean?
2. Where is the P0321 sensor located?
3. What are the common causes of code P0321 ?
4. Get Help with P0321

What Does Code P0321 Mean?

OBD II fault code P0321 is a generic code that is defined as “Crankshaft position (CKP) sensor/engine speed (RPM) sensor range/performance problem”, and is set when the PCM (Powertrain Control Module) detects an input signal from the crankshaft position (CKP) sensor/engine speed (RPM) sensor that is erratic, implausible, or falls outside of expected parameters.

NOTE #1: Note that on older applications that still use distributors, this code may be displayed as P0321 – “Ignition/Distributor Engine Speed Input Circuit Range / Performance”, which means exactly the same as the definition given above.

NOTE #2: On VAG group applications, this code may be displayed as “16705/P0321/000801 – Engine Speed Sensor (G28): Implausible Signal”, which means exactly the same as the two other definitions given above.

NOTE #3: On most modern applications, the Crankshaft position (CKP) sensor does double duty, and is used to monitor the engine speed in addition to providing input data on the position of the crankshaft to the PCM for the purposes of calculating ignition timing and fuel delivery strategies.

The primary purpose of the CKP (crankshaft position) sensor is to provide precise input data to the PCM regarding the rotational angle of the crankshaft. Without this information, the PCM is not able to calculate an appropriate ignition timing, and hence, an appropriate fuel delivery strategy.

In practice, most applications use a reluctor ring (that is attached to the crankshaft), and (most commonly) a Hall-effect sensor whose induced magnetic field is interrupted by the teeth on the reluctor ring as the ring rotates. Since the teeth on the reluctor ring are evenly spaced, the PCM is able to “count” the number of times the sensor’s magnetic field is interrupted, which information is used to both calculate the engine speed, and the position of the crankshaft.

However, all reluctor rings have a spot where one tooth is “missing”, thus creating a gap that is twice as wide as the gaps between all other teeth. This gap however, is located relative to piston #1, which means that the gap serves to indicate to the PCM where piston #1 is in its upward motion during the compression stroke. In practical terms, the regular on/off square waveform pattern that is created when the reluctor ring rotates is “broken” when the wider gap in the reluctor ring’s teeth passes in front of the CKP, thus creating a reference point during each revolution of the engine that the PCM uses to calculate ignition timing and fuel delivery strategies.

While the above is a gross over simplification of a very complex process, it should serve to illustrate the point that without accurate input data regarding the position of the reference point on the reluctor ring i.e., the position of the crankshaft relative to piston #1, the PCM is unable to determine when to deliver a spark and fuel not only to cylinder #1, but to all cylinders. Thus, when the PCM detects an input voltage from the CPS that falls outside of expected parameters, or is abnormal in any way, it will recognize that it cannot control the ignition and fuel delivery systems effectively, and it will set code P0321 as a result.

Note that whether or not a warning light is illuminated when code P0321 sets depends on both the application and the severity of the problem.

Where is the P0321 sensor located?

The image above shows a typical reluctor ring and Crank Position Sensor. Note that while the reluctor ring is attached to the crankshaft at the front of the engine in this example, the reluctor ring can be mounted on the flywheel between the engine and transmission on some applications. On still other applications, the reluctor ring may be mounted on the crankshaft inside the crank case.

Always refer to the manual for the affected application to locate and identify the crankshaft position sensor correctly. Failure to do this could lead to a misdiagnosis, and the unnecessary replacement of parts and components.

What are the common causes of code P0321 ?

Note that if other codes, and especially codes that are related to misfires or unmetered air entering the engine are present along with P0321, these codes MUST be resolved before a diagnosis of P0321 in attempted, since misfires can cause changes or variability in the signal voltages of CPS sensors on many applications. Nonetheless, some common causes of code P0321 could include the following-

• Defective CPS sensor
• Damaged, burnt, shorted, disconnected, or corroded wiring and/or connectors in the CPS sensor control/signal circuit
• Defective or damaged reluctor ring
• Clogged teeth on the reluctor ring
• Failed or failing PCM. Note that this is a rare event, and the fault must therefore be sought elsewhere before any control module is replaced

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