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2005 Mercury Mariner 3.0L Engine Misfiring: P0351, P0353, P0354 Codes After Coil Replacement

Model: 2005 Mercury Mariner Fault Code: P0351 Posted: 2015-03-10 07:46

I replaced three ignition coils on my 2005 Mercury Mariner 3.0L engine, and after the replacement, the OBD2 diagnostic codes disappeared temporarily. However, the engine continues to misfire. When I disconnected the coil in position D, there was no improvement in performance. In fact, disconnecting the coils in positions E and F made the engine run rougher. After disconnecting those coils, the fault codes P0351, P0353, and P0354 (Primary/Secondary Circuit) reappeared. I've tried moving the ignition harness around, but no change was observed. A second mechanic suggested that the Powertrain Control Module (PCM) may need to be replaced. Despite this, I'm unsure whether the issue lies with the coils, wiring, or another component. What could be causing these persistent misfire codes and erratic engine behavior?

Related fault codes
P0351P0353
Comments (2)
Anonymous 2015-03-10 08:09

This situation is confusing — you replaced three coils and reported no codes afterward. Why were those specific coils replaced? Disconnecting a coil to test it may actually be the root cause of the P0351, P0353, and P0354 codes appearing. Replacing the PCM is not typically the first step; it should only be considered if all other diagnostics fail.

Anonymous 2015-03-10 09:07

This issue can be addressed through a basic diagnostic procedure. The 2005 Mercury Mariner 3.0L has six ignition coils, each with two wires — one common (12V) and one signal wire. Here's how to test: Test 1: With the engine off, disconnect each coil and use a test light to check for 12 volts on the red (common) wire. Repeat this for all six coils. Test 2: Connect a test light between the common wire and the signal wire (colored differently). Crank the engine — the light should flash intermittently. If it doesn't flash, that indicates a faulty coil or wiring issue. This step helps identify which coil is not functioning properly.