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OBD II Fault Code

  • OBD II P0351 Ignition Coil "A" Circuit  Primary/Secondary Malfunction
The ignition coil or coils are responsible for igniting the air/fuel mixture inside the combustion chambers. Without reliable performance from the ignition coil(s) the vehicle will stumble and misfire. 

Code P0351 indicates there's an electrical problem in either the primary ( the computer side ) or the secondary ( the spark plug side ) of the Ignition Coil "A" Circuit. 

P0351 Symptoms

  • Check Engine Light will illuminate
  • Engine idles rough
  • Engine misfires on acceleration
  • In rare cases, the engine may not exhibit noticeable symptoms

Common Problems That Trigger the P0351 Code

  • Defective Ignition Coil(s)
  • Defective Spark Plug(s)
  • Intake Manifold Vacuum leaks
  • Carbon buildup in the Throttle Body air passages
  • Defective Idle Air Control Valve or Electronic Body

Common Misdiagnosis

  • Ignition coil(s) replaced when cause of the malfunction was a vacuum leak
  • Spark Plugs replaced when cause of the malfunction was a vacuum leak

P0351 Diagnostic Theory for Shops and Technicians

When the code P0351 is set in the Powertrain Computer, it means that the Powertrain Computer or PCM is not seeing the proper electrical signals from the ignition coil(s) during normal operation. This can be caused by problems on either the primary (computer) side or the secondary (spark plug boot, spark plug wire and/or spark plug itself ) side.  

When diagnosing a P0351 code, it is important to record the freeze frame information and then to duplicate the code setting conditions with a test drive. Pay close attention to the engine load, throttle position, RPM, and road speed. Road test the vehicle while viewing the misfire PID information on a data streaming scanner. If the vehicle is misfiring then you may have verified code P0351. Be sure to verify the the steadiness of the crank signal, because this can cause all kinds of downstream problems. If the vehicle deploys a multiple direct coil ignition system, locate the offending coil. Switch the entire coil and spark plug as an assembly with a known good cylinder, Clear the code(s) and go for a test drive. If the code re-sets and follows the coil assembly that was moved, then you may have verified the cause of the P0351 code. If the same cylinder sets the code, then perform a compression test on the offending cylinder and check for any vacuum leaks in its area with a good quality smoke machine.  If the compression and smoke test results are good, then check the connector and wiring for that cylinder's coil circuit. If the connector and circuitry are good, then test the coil firing signal with a labscope, because the coil driver circuit may be defective. 


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1 User Comment

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By , August 25, 2017
I have had a problem with my 2001 Jeep Grand Cherokee since I have owned it (about 8 months). Occasionally, it will run so rough that it is not drive-able, or even stalls. When this happens, turning it off (if it didn't stall) and turning it on again will either solve the issue for the rest of the trip, or improve the situation enough that the car is drive able. Sometimes (but not always) this condition will cause the check engine light to illuminate, and generally the Codes indicate that the their were misfires on several or all of the cylinders. (I didn't need an analyzer to figure that out.) Recently it stalled and would not start. While waiting for a tow truck to arrive (about 10 minutes), I tried starting and it started up. Bob's my uncle for the trip home. When I got home I had the following codes (in addition to misfire codes): P3051, P3052, P3053. Also I thought I smelled silicone for part of the trip both before and after the stall, but it went away (40 mile trip). Does this narrow down the possible causes of the P3051-P3053 codes?