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2005 GMC Sierra 1500 P0351 Code: No Misfire, Spark Plug Replacement, and Intermittent Ignition Issues

Model: 2005 GMC Sierra 1500 Fault Code: P0351 Posted: 2016-08-02 19:26

My 2005 GMC Sierra 1500 (4.3L V6, 5-speed manual) died while driving and was towed home. The vehicle has been running fine since, but the check engine light remains on with a persistent P0351 code indicating ignition coil primary circuit malfunction. I replaced both the ignition control module (ICM) and the spark plug assembly (AC Delco Iridum, gap set to 0.060 inches). After each replacement, I cleared the code using an OBD-II scanner, restarted the engine, and the P0351 code returned immediately. I've verified that: - The spark plugs are new and correctly gapped. - All connectors are tight, corrosion-free, and properly seated. - There are only two wires at the coil connector (not three), which is consistent with factory wiring for this model at 120,000 miles. - The pink wire (terminal A) shows steady 12V when connected to the battery. - The white/black wire (terminal C) appears to be a signal line from the coil to ICM — however, voltage readings on this wire are erratic and unstable during engine cranking. Despite no misfire symptoms or performance issues, the P0351 code persists. I’ve ruled out aftermarket spark plugs as a cause, and have replaced both coils with OEM units (both have three-prong connectors but only two wires are present in the harness). I’m concerned that the issue may not be related to the coil itself or wiring, but rather an intermittent loss of voltage in the ignition circuit — possibly due to poor connections at specific fuse blocks or harness junctions. According to a TSB (Technical Service Bulletin) for 2005–2006 GMC Sierra and Savana models with V8 engines (RPO codes LR4, LM7, LQ4, LQ9), if P0351 persists without a clear cause, a wiggle test should be performed on the ignition coil harnesses to detect intermittent voltage loss. Key circuits to inspect include: - S160 and S159 (for C/K trucks) - C148 and C149 (especially for pink power feed circuit) I have no access to a high-end scanner with freeze frame data or advanced diagnostics, so I’m seeking community input on whether this could be a wiring issue, sensor fault, or an intermittent coil pickup problem. Any guidance on how to perform the wiggle test or where to focus inspection would be greatly appreciated. Note: I have not found any official documentation confirming that the 2005 GMC Sierra 1500 requires a three-wire coil connector — this has been consistent throughout its life, even at 120,000 miles.

Related fault codes
P0351
Comments (12)
Anonymous 2016-08-03 11:29

Start with the ignition coil wiring. The two wires are typically pink (terminal A, 12V) and white/black (terminal C, signal to ICM). Terminal B is not always used. Confirm that your 4.3L engine has these correct wire colors. Check if terminal A shows steady 12V and whether the white/black wire receives a stable signal from the ICM. This will help determine if the issue lies in wiring or signal integrity.

Anonymous 2016-08-05 17:05

Confirmed: engine is 4.3L with correct wire colors. Pink wire (terminal A) reads steady 12V. White/black wire (terminal C) shows inconsistent voltage — appears random and unstable during cranking, suggesting a possible intermittent signal issue.

Anonymous 2016-08-05 17:05

No other diagnostic codes are present on the OBD-II scanner. The vehicle runs smoothly with no misfires or performance issues.

Anonymous 2016-08-06 09:54

Since there's no misfire but a persistent P0351 code after replacing both ICM and coil, it’s likely not a primary ignition failure. The white/black wire carries an AC signal from the coil to the ICM — if this signal is unstable or intermittent, it could trigger the code even without visible misfires. Some aftermarket spark plugs (e.g., Bosch) can cause issues; you used AC Delco Iridum, which should be compatible. Still, verify plug resistance and wire integrity.

Anonymous 2016-08-06 11:00

I replaced the spark plugs while waiting for parts — they were AC Delco Iridum with gap adjusted to 0.060 inches. After installing a new ICM, the engine started fine but immediately triggered P0351 again upon restart. This suggests the issue is not in the spark plug or ignition timing, but rather in the signal path between coil and ICM.

Anonymous 2016-08-06 12:44

New plugs should be fine — they are correct for this engine. The fact that P0351 persists after both ICM and coil replacement with no misfire is unusual. It points to a deeper issue, possibly in the wiring harness or sensor. Confirm whether your scanner reads all codes (including manufacturer-specific ones like P1351) and if it captures freeze frame data — this would help identify intermittent conditions.

Anonymous 2016-08-06 13:51

I tested voltage on both pink and white/black wires during cranking. The ICM output was unstable, with rapid fluctuations. My scanner is a basic OBD-II tool without freeze frame or advanced diagnostics — I don’t have access to a shop that can perform high-end scans. This makes troubleshooting difficult.

Anonymous 2016-08-06 14:57

The white/black wire likely carries an AC signal from the coil, not direct power. To test this: unplug the ICM’s probe (white) wire — do NOT disconnect the white/black wire. Crank the engine and use a multimeter to check for 1–4V AC on the pink wire. If you see stable AC voltage in that range, it confirms proper signal flow; if not, there may be an issue with the ICM or coil harness.

Anonymous 2016-10-15 14:50

Back again — same problem persists. P0351 returns after every clear and restart. All voltage readings were checked and appear normal. The vehicle runs smoothly with no misfire. No other codes are present. I’m at a loss as to what could be causing this intermittent code without any performance issues.

Anonymous 2016-10-27 10:51

Any further suggestions or troubleshooting steps would be very helpful — especially for a basic OBD-II scanner user with limited access to professional diagnostics.

Anonymous 2016-10-27 15:04

After researching, I found a TSB (PIP 3893A) for 2005–2006 GMC Sierra and Yukon models with V8 engines. If P0351 persists without clear cause, perform a wiggle test on the ignition coil harnesses to detect intermittent voltage loss. Key areas to inspect: - S160 and S159 (C/K trucks) - C148 and C149 (especially pink power feed circuit) - Check for broken insulation or loose connections in harnesses If any issues are found, follow the SI repair procedures. Even if symptoms resolve early, complete all steps to ensure full diagnosis.

Anonymous 2017-08-14 22:15

I’ve seen similar intermittent P0351 cases where a coil position sensor (coil pickup) was the root cause — especially after replacing multiple sensors and coils. While this model doesn’t have a traditional coil pickup, it’s worth checking for any sensor-related issues that could mimic ignition faults. A faulty pickup or signal sensor may trigger false codes without visible misfires.