Diagnose & Clear P1351 with iCarsoft CR MAX: Fix Ignition Coil Control Circuit Issues

If your check engine light illuminates and a scan returns P1351, your vehicle is signaling a problem with its ignition system. This manufacturer-specific code—common in GM, Ford, and Chrysler vehicles—typically indicates an "Ignition Coil Control Circuit High Voltage (Bank 1, Cylinder 1)" or a similar issue with the ignition coil driver circuit.

The ignition coil converts low-voltage battery power into the high voltage needed to ignite fuel in the combustion chamber. Modern systems use coil-on-plug or coil packs controlled by the Engine Control Module (ECM), which sends precise timing signals to trigger spark. When P1351 occurs, the ECM detects abnormally high voltage in the control circuit for Bank 1, Cylinder 1’s coil, disrupting spark timing and causing misfires, reduced power, or even stalling.

Basic scanners might only flag "ignition coil fault" but can’t isolate whether the issue is a faulty coil, damaged wiring, or a failing ECM driver. The iCarsoft CR MAX solves this with vehicle-specific ignition system diagrams, real-time coil voltage monitoring, and active circuit tests. Let’s walk through how to diagnose and resolve P1351.

Why It Matters

Ignoring P1351 risks more than just a lit check engine light—it undermines your engine’s performance and risks expensive damage. The ignition coil’s role in spark generation is critical: a disrupted control circuit for Cylinder 1 leads to incomplete combustion, wasted fuel, and increased emissions. Over time, unburned fuel can overheat the catalytic converter (costing $800–$1,500 to replace) and cause premature wear on spark plugs, pistons, and valves.

In severe cases, P1351 can cause persistent misfires that make the engine undriveable. Addressing it promptly with the iCarsoft CR MAX not only restores smooth operation but also prevents cascading failures that drain your wallet.

Understanding P1351: Causes & Key Symptoms

To diagnose P1351 effectively, first break down the ignition coil control system and its failure triggers:

Key Symptoms of P1351

• Illuminated Check Engine Light: The primary indicator—activates when the ECM detects control circuit voltage exceeding 10V for 3+ consecutive seconds.
• Engine Misfire: Notable misfire in Cylinder 1, felt as rough idle, shaking during acceleration, or hesitation under load.
• Reduced Power & Performance: Noticeable loss of acceleration, especially at low RPMs where ignition timing is most critical.
• Increased Fuel Consumption: Unburned fuel from misfires leads to 10–15% worse fuel economy.
• Catalytic Converter Risk: Unburned hydrocarbons (HC) overheat the catalytic converter, potentially causing it to melt or fail.

Common Causes of P1351

Why iCarsoft CR MAX Excels at Diagnosing P1351

Basic OBD-II scanners can’t decode P1351’s make-specific nuances, but the iCarsoft CR MAX is tailored to GM, Ford, and Chrysler ignition systems:

Step-by-Step: Diagnose P1351 with iCarsoft CR MAX

1. 1. Connect & Confirm the Code

   Plug the CR MAX into your vehicle’s OBD-II port (under the dashboard) and power it on. Select your vehicle via Auto VIN (fast and accurate) or manual entry (make/model/year). Navigate to Engine > Fault Codes > Read Codes to confirm P1351. Tap Code Details for vehicle-specific insights (e.g., "GM: Ignition Coil 1 Control Circuit Voltage High" or "Ford: Cylinder 1 Coil Driver Circuit Open").

2. 2. Check for Related Codes

   P1351 rarely appears alone—scan for companion faults to narrow the root cause:
   - P0300: Random/Multiple Cylinder Misfires
   - P0301: Cylinder 1 Misfire Detected
   - P1350/P1352: Other Ignition Coil Circuit Faults (e.g., Cylinder 2, 3)
   - P0607: ECM Internal Control Module Performance
   Address these first—multiple codes often indicate a shared issue (e.g., bad ground or ECM problem).

3. 3. Locate Bank 1, Cylinder 1 Ignition Coil

   Use the CR MAX’s Component Location tool to identify Bank 1 (usually the cylinder bank containing cylinder #1; check diagrams for your engine):
   - GM V8: Bank 1 is driver’s side (left)
   - Ford V6: Bank 1 is passenger’s side (right) for some models
   - Chrysler Inline-4: Bank 1 is the only bank
   Locate Cylinder 1’s coil: Coil-on-plug systems have individual coils; coil packs have a shared unit with labeled terminals (e.g., "C1" for Cylinder 1).

4. 4. Monitor Live Ignition Data

   Use the CR MAX’s real-time data to spot voltage irregularities:
   1. Go to Engine > Live Data > Ignition System and select:
   - "Ignition Coil 1 Control Voltage" (should pulse between 0V–12V as the ECM triggers the coil)
   - "Cylinder 1 Misfire Count" (increases with P1351-related misfires)
   2. Start the engine and observe:
   - Sustained voltage >10V = short in coil or wiring
   - No voltage pulse = broken wire or ECM driver failure
   - High misfire count = confirmed Cylinder 1 ignition issue

5. 5. Inspect the Coil & Wiring

   Visually examine the ignition coil and its harness for physical damage:
   - Coil Body: Look for cracks, oil contamination (sign of leaking valve cover gasket), or burn marks (indicates overheating).
   - Electrical Connector: Inspect for green/white corrosion, bent pins, or loose terminals—clean corroded connectors with electrical contact cleaner.
   - Wiring Harness: Check for frayed insulation, cuts, or damage where the harness rubs against engine components (e.g., exhaust manifolds).

6. 6. Test the Ignition Coil

   Use the CR MAX to run targeted resistance tests on the coil:
   1. Navigate to Special Functions > Engine > Ignition Tests > Coil Resistance Test
   2. Select "Cylinder 1" and follow prompts to measure:
   - Primary Resistance: Normal range: 0.5–2.0Ω (varies by make/model—consult CR MAX’s specs)
   - Secondary Resistance: Normal range: 8,000–15,000Ω
   3. Result: Readings outside specs = faulty coil
   4. Swap Test (If Safe): Swap Cylinder 1’s coil with another cylinder (e.g., Cylinder 2) using the CR MAX’s diagram. Rescan: P1350/P1352 appears = faulty coil (replace it); code remains = wiring/ECM issue.

7. 7. Test the Control Circuit

   Wiring issues often mimic coil failures—use the CR MAX to verify circuit integrity:
   1. Go to Special Functions > Engine > Circuit Tests > Ignition Coil Control Circuit
   2. Test for:
   - Short to Power: Unexpected 12V when coil is inactive (indicates wiring touching power source)
   - Open Circuit: No continuity between coil and ECM (broken wire)
   - Ground Integrity: Resistance <0.5Ω (high resistance = corroded ground)
   3. Fixes: Repair frayed wires with heat-shrink connectors; replace severely damaged harnesses; clean/re-tighten ground connections.

8. 8. Check for ECM Issues

   If coil and wiring test good, the ECM’s driver circuit may be faulty:
   1. Use the CR MAX’s ECM Communication Test to verify the module receives/sends signals properly.
   2. Check for technical service bulletins (TSBs) via the CR MAX’s Service Info—some manufacturers offer ECM reflashes for P1351-related software bugs.
   3. Professional Help: If tests indicate ECM failure, consult a shop for reflashing or replacement (OEM ECMs cost $300–$800, plus programming).

9. 9. Repair & Clear P1351

   Fix the root cause based on diagnostics:
   - Faulty Coil: Use the CR MAX’s Part Lookup to find OEM coils (e.g., AC Delco D510C for GM, Motorcraft DG511 for Ford).
   - Wiring/Connectors: Repair as noted in Step 7; apply dielectric grease to connectors to prevent future corrosion.
   - ECM Issues: Have the ECM reflashed or replaced by a professional.
   Clear the code: Navigate to Engine > Fault Codes > Clear Codes to delete P1351.

10. 10. Verify the Repair

    Take a 15-minute test drive, including:
    - Idle periods to check for smooth operation
    - Acceleration tests to monitor for hesitation/misfires
    - Highway driving to ensure consistent performance
    Use the CR MAX’s Data Logging to record coil voltage and misfire counts during the drive. Re-scan after: No return of P1351 + zero misfires = successful repair; code return = revisit coil/wiring tests or ECM diagnostics.

Preventing P1351 Recurrence

Use the iCarsoft CR MAX to maintain a healthy ignition system and avoid future P1351 faults:

• Coil Inspections: Include in routine tune-ups—check for oil leaks from valve cover gaskets that can damage coils.
• Wiring Checks: Inspect ignition harnesses during oil changes; secure loose sections away from heat sources (e.g., exhaust pipes).
• Connector Maintenance: Apply dielectric grease to coil connectors annually to repel moisture and prevent corrosion.
• ECM Updates: Use One-Key Upgrade to install ignition system calibration updates—fixes software bugs that cause false P1351 codes.
• Spark Plug Replacement: Worn plugs strain coils—replace per manufacturer intervals (typically 30,000–100,000 miles).

Summary Table