SAE Standard OBD-II Universal Error Code P0172

SAE Standard OBD-II Major Misfire

Model: OBD-II Universal | Code: P0172

Applicable Systems

OBD-II Universal

Symptoms

The engine control module has detected a cylinder misfire. The check engine light flashes and the engine runs rough with reduced power.

Step 1: Connect an OBD-II scanner and read the misfire code (P0301-P0312)
The last digit identifies the misfiring cylinder number
Step 2: Swap the ignition coil from the misfiring cylinder to a known-good cylinder
If the misfire follows the coil, replace the coil
Step 3: Remove and inspect the spark plug for fouling, wear, and gap
Replace if worn; set the gap to the specification in the service manual
Step 4: If the ignition system is good, perform a compression test on the misfiring cylinder
Low compression indicates valve, piston ring, or head gasket issues

Reset: Clear the code with the OBD-II scanner after the repair. The check engine light turns off after 3 consecutive drive cycles without a misfire.

Spark plug: Iridium or platinum, pre-gapped (Match to engine specification)
Ignition coil: Coil-on-plug or dual-post (Match to engine model)
OBD-II scanner: Compatible with the vehicle protocol (For code reading and clearing)

Q: What is a misfire?
Incomplete or absent combustion in one or more cylinders. Causes include ignition, fuel, compression, or timing problems. Persistent misfire can damage the catalytic converter.
Q: How do I identify the misfiring cylinder?
Read the DTC. P0301 = cylinder 1, P0302 = cylinder 2, etc. P0300 = random/multiple cylinder misfire.
Q: Can I drive with a misfire?
Briefly to reach a service area. Prolonged driving with a misfire can overheat and damage the catalytic converter, leading to expensive repairs.