P1373 — Ignition Spare

What is the most common cause of P1373?

The most common causes are: faulty ignition control circuit in the ECM, worn spark plugs or wrong plug gap, failed ignition coil or coil pack.

What are the symptoms of P1373?

Drivers most often notice: increased fuel consumption, misfires under load or at idle, hard starting, especially in damp weather, loss of power and jerking.

How do I diagnose P1373 myself?

Start with a scan: confirm P1373, save the freeze frame and note any companion codes. Then inspect the wiring and connectors related to the ignition system, and verify the suspect component against live data before buying parts.

What does OBD2 code P1373 mean?

Ignition Spare (P1373): a powertrain (engine/transmission) fault affecting the ignition system. Short, gentle driving to a shop is usually possible. Most often caused by faulty ignition control circuit in the ECM, worn spark plugs or wrong plug gap, failed ignition coil or coil pack.

How much does it cost to fix P1373?

Replace spark plugs — $90–$250; Replace an ignition coil — $150–$380; Repair coil wiring or connector — $80–$250. Exact cost depends on the root cause, your vehicle and local labor rates — a proper diagnosis is the cheapest first step.

When your vehicle's engine computer detects something wrong with the firing sequence, it often stores a P1373 trouble code. This particular code flags an ignition spare fault, meaning the PCM has identified abnormal behavior in the ignition system that goes beyond a simple miss-fire. The powertrain control module monitors the voltage and timing signals sent to the ignition coils, and when those signals fall outside expected parameters, P1373 gets triggered. Unlike codes that appear from a single glitch, this one requires the fault to repeat under specific operating conditions before the check engine light activates. That pattern matters when you're diagnosing it, because it means the problem is consistent rather than intermittent.

The freeze frame data saved alongside P1373 is your roadmap. When the code sets, the computer records engine load, RPM, coolant temperature, and vehicle speed at that exact moment. Those readings tell you precisely what conditions caused the fault, whether it happens at idle, under hard acceleration, or during cold starts. Use that data to recreate the scenario when testing. The ignition system in modern engines relies on precise timing between the crankshaft position sensor, cam position sensor, and the PCM's command to the coil. When any part of that chain breaks down electrically, the engine runs poorly and emissions rise.

Once P1373 sets, you'll likely notice the engine stumbling, especially under throttle load. Misfires become audible as a rough idle or hesitation during acceleration, and fuel economy drops noticeably because unburned fuel gets pushed through the exhaust. Damp or rainy weather often makes hard starting worse if moisture has entered the spark plug wells or coil connectors. The check engine light stays illuminated, and in some cases you may feel a jerking sensation or notice a lack of power compared to normal driving. These symptoms point directly to an ignition problem rather than a fuel or emissions issue, though the code itself focuses on the electrical side of the firing system.

Symptoms

• Check engine light remains on after startup
• Engine misfires noticeably at idle or under load
• Hard starting, particularly in humid or wet conditions
• Noticeable loss of engine power and hesitation during acceleration
• Increased fuel consumption compared to your normal driving pattern
• Rough running or jerking sensations when the engine is under stress

Most often, the root cause of P1373 traces back to a failing ignition coil or coil pack. These components take a beating from heat, vibration, and voltage demands, so they eventually break down. Moisture or oil contamination in the spark plug tube wells creates a short path that disrupts the high-voltage circuit. Damaged wiring or corroded connectors in the coil control circuit prevent the PCM from properly firing the plugs. In rarer cases, the ignition control circuitry inside the ECM itself develops a fault, though that represents a much less common scenario than external hardware failures.

Common Causes

• Failed ignition coil or coil pack (most frequent cause)
• Moisture or engine oil leaking into the spark plug wells
• Damaged or chafed wiring harness feeding the ignition coils
• Corroded or loose electrical connectors at the coil mount
• Faulty ignition control circuit within the engine control module
• Worn or incorrectly gapped spark plugs allowing weak sparks

Before spending money on parts, run through a systematic diagnostic sequence. Connect an OBD2 scanner and verify that P1373 is the active code, then record the freeze frame data so you know exactly what engine conditions triggered it. Scan for any other stored codes as well, because related faults often point to the real culprit. Check for any manufacturer technical service bulletins that apply to your specific make and model, since some ignition issues have known factory fixes or software recalibrations. Visually inspect the entire ignition wiring harness for damaged insulation, melted sections near heat sources, or loose connections at each coil. Pull the suspected coil and swap it to a different cylinder to see if the fault code moves with it, which confirms a bad coil versus a wiring problem. Examine the spark plugs for oil fouling, carbon deposits, or improper gap spacing. After repairs, clear the code and drive the vehicle through the exact conditions recorded in the freeze frame to verify the problem is resolved.

How to Diagnose P1373

1. Connect an OBD2 scanner, confirm P1373 is stored, and record the freeze frame data showing engine conditions when the fault occurred.
2. Check for additional diagnostic trouble codes and research TSBs for your vehicle make and model using the manufacturer website or NHTSA database.
3. Perform a thorough visual inspection of all ignition coil wiring, paying close attention to connector pins for corrosion and the harness for any damaged sections.
4. Test the suspected coil by swapping it with a known good unit from another cylinder and observe whether the fault code migrates.
5. Remove and inspect spark plugs for signs of wear, oil contamination, carbon tracking, or incorrect electrode gap.
6. Clear the code after any corrective action, operate the vehicle through the freeze frame conditions, and confirm P1373 does not return.

Once you've isolated the problem, repair costs vary depending on which component failed. Spark plug replacement runs between $90 and $250 when done at a professional shop, covering parts and labor for a full set. An individual ignition coil replacement typically costs $150 to $380 depending on your vehicle and whether you use OEM or aftermarket parts. Wiring harness repair or connector replacement generally falls in the $80 to $250 range depending on how extensive the damage is and how much labor the job requires.

Repair Options

• Spark plug replacement (full set): $90–$250
• Ignition coil or coil pack replacement: $150–$380
• Wiring harness repair or connector replacement: $80–$250

Most independent shops charge between $80 and $380 total to resolve P1373, with the exact figure depending on whether plugs, coils, or wiring need attention. Labor rates vary by region, but diagnosis typically runs one to two hours of shop time. Skip the temptation to replace expensive components first; verify which part is actually faulty through proper testing to avoid wasting money on parts that aren't the source of the problem.

Driving Safety Verdict

P1373 carries a caution severity rating. The misfires caused by ignition faults introduce unburned fuel into the exhaust stream, which overheats and destroys the catalytic converter over time. Avoid hard acceleration or heavy loads until the problem is repaired. If the check engine light begins flashing, stop driving immediately and have the vehicle towed to a shop—continuous misfiring can cause rapid catalytic converter failure and create a fire hazard.