P1302 – Cylinder Number 2 Random Misfire Detected (Acura, Honda)

By Reinier (Contact Me)
Last Updated 2022-02-07
Automobile Repair Shop Owner

Manufacturer Specific Definitions for P1302

Table of Contents

1. What Does Code P1302 Mean?
2. Where is the P1302 sensor located?
3. What are the common causes of code P1302?
4. What are the symptoms of code P1302?
5. Get Help with P1302

What Does Code P1302 Mean?

OBD II fault code P1302 is a manufacturer-specific trouble code that is defined by carmakers Honda and Acura as, “Cylinder Number 2 Random Misfire Detected”, and is set when the PCM (Powertrain Control Module) detects a random or non-cyclical misfire in cylinder #2.

NOTE: Random or non-cyclical misfires in any cylinder are misfires that occur without a pattern. In practice, the misfires appear randomly, and often under different operating conditions and/or under varying environmental conditions, which can make it difficult to replicate and or diagnose the root cause of the problem. Cyclical misfires, on the other hand, are misfires in any cylinder that occur at every engine cycle i.e., the air/fuel mixture fails to ignite, or the mixture ignites only partially at the end of every compression stroke.

As on most other vehicle makes, Honda and Acura vehicles use the crankshaft position sensor to detect misfires, and in the broader context of the engine management system, this application of the crankshaft position sensor forms the basis of the misfire detection system. Here is how the misfire detection system on Honda and Acura vehicles works in practice-

The crankshaft position sensor works in conjunction with a reluctor wheel on the harmonic balancer (crankshaft pulley) to generate electrical signals as the teeth on the reluctor ring’s teeth move past the sensor’s sensing element. We need not delve into the different types of crankshaft sensors in use on Honda and Acura vehicles here, beyond saying that the electrical signals serve two purposes. The first is that the CPM uses the signals as triggers to initiate ignition sparks, and the second is that a fixed reference point on the reluctor ring is used to calculate the position of piston #1 during cranking before the engine starts.

Refer to the image below; in this image, the large orange arrow indicated the actual crankshaft position sensor relative to the reluctor ring, while the small yellow arrow indicates a tooth on the reluctor ring moving past the sensing element in the crankshaft position sensor. However, the important thing to note here is that the distance between the tooth indicated by the yellow arrow and the first tooth indicated by the red circle is slightly larger than the distance between the two teeth indicated by red circles.

This difference produces a slightly different signal, which the PCM interprets as the position of cylinder #1 during both engine cranking, and normal engine operation, and it is this reference point the PCM uses to identify misfires on one or more cylinders.

In practice, the crankshaft rotates at a reasonably constant rate on an engine that is not misfiring, but if a misfire occurs, the misfire produces small variations in the crankshaft’s rotational speed during each revolution of the crankshaft. Note, though, that as a general rule, the PCM ignores speed variations that are smaller than about 2 percent of the crankshaft’s average rotational speed, since all crankshafts undergo small deformations and vibrations during normal engine operation.

As a practical matter, all misfire detection systems use complex algorithms that are based on the number of teeth of the reluctor ring, and the more teeth a reluctor ring has, the higher the resolution of the ignition timing calculation becomes, which greatly increases the accuracy of the misfire detection system.

Nonetheless, if the misfire detection system detects a variation in the crankshaft’s rotational speed that exceeds a maximum allowable threshold, it “notes” the position of the variation (measured in degrees of crankshaft rotation) relative to the fixed reference point on the reluctor ring. This position forms the basis of the calculations the PCM performs to identify the misfiring cylinder, which in the case of OBD II code P1302 on Honda and Acura vehicles, is cylinder #2.

Note that in case of persistent, cyclical misfires, the PCM will typically disable the fuel injector on the affected cylinder to protect the catalytic converter(s). However, with random misfires, the PCM may not always disable the injector on the affected cylinder when a misfire occurs, which could eventually damage or even destroy the catalytic converter(s) if the fault persists for extended periods.

Thus, when the PCM detects a random misfire on cylinder #2 (or on any other cylinder(s)), it will set code P1302, and illuminate a warning light after a pre-defined number of ignition failures or misfires had occurred.

Where is the P1302 sensor located?

This image shows the location of the crankshaft position sensor on a Honda Civic application. Note that while the crankshaft position sensor is typically located close to the harmonic balancer (crankshaft pulley), it may be difficult to access the sensor on some Honda and/or Acura applications.

In some cases, it may be necessary to remove and/or disassemble unrelated parts and/or components such as the drive belt, alternator, radiator, coolant hoses, HVAC lines, power steering lines, and other parts simply to gain sufficient workroom to remove the plastic timing cover that covers and protects the crankshaft position sensor and timing belt.

Thus, if you suspect that the problem might be caused by a defective crankshaft position sensor and/or a damaged reluctor ring, we recommend that you consult reliable service information for the affected application to prevent damage to any parts and/or components during the disassembly process.

What are the common causes of code P1302?

While cyclical or persistent misfires Honda and Acura applications could have a large number of possible causes, random misfires on these applications are typically caused by a limited number of issues, defects, and/or malfunctions. Nonetheless, some possible causes of random misfires on Honda and Acura applications could include one or more of the following-

• Defective or intermittently malfunctioning spark plug
• Defective or intermittently malfunctioning ignition coil
• Defective or intermittently malfunctioning crankshaft position sensor
• Intermittent defects and malfunctions in the primary ignition circuit of cylinder #2. Such defects include burnt, shorted, damaged, and corroded wiring and /or electrical connectors
• Intermittent defects and/or malfunctions in the fuel injector on cylinder #2
• Defects in the injector’s wiring, with possible defects including burnt, shorted, damaged, and corroded wiring and /or electrical connectors
• Intermittent engine vacuum leaks, such as localized failures of intake manifold gaskets and/or seals that only affect cylinder #2
• In rare cases, some mechanical issues, such as randomly sticking or binding valves might cause random misfires to occur on affected cylinders
• PCM issues, such as intermittent malfunctions of the ignition driver for cylinder #2
• Defective or corrupted software in the PCM, but note that this will a) rarely affect only one cylinder, and b), seldom cause random misfires, since corrupted software is typically far more likely to cause persistent, cyclical misfires. Note, though, that while there are exceptions to this rule, the fault must first be sought elsewhere before any control module is reprogrammed or replaced

What are the symptoms of code P1302?

Common symptoms of code P1302 could include one or more of the following, but note that depending on the engine speed/load, the severity of some symptoms may vary between different engine designs.

• Stored trouble code and possibly an illuminated warning light
• Depending on the nature of the problem, one or more additional codes may be present along with P1302
• The engine may stumble or hesitate momentarily under acceleration
• Depending on the nature and severity of the problem, the engine may run roughly at idling speed
• In some cases, and depending on both the engine design and the engine speed/load, the misfire may disappear, or the misfire may not be apparent at high engine speeds and/or high engine loads
• In some cases, catalytic converter damage could result if the problem is not found and corrected promptly

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