B1370 — Ignition Tach Circuit Short To Ground

Will B1370 clear itself?

Sometimes B1370 clears after a few drive cycles if the fault was intermittent — for example a loose connector or a tank of bad fuel. The underlying cause usually remains, so the code tends to return. Clear it once; if it comes back, diagnose rather than erase it repeatedly.

What is the most common cause of B1370?

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

How much does it cost to fix B1370?

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

Is it safe to drive with B1370?

Drive with caution and avoid load. Ignition faults cause misfires that quickly overheat and destroy the catalytic converter; if the Check Engine Light flashes, stop and fix it first.

What are the symptoms of B1370?

Drivers most often notice: hard starting, especially in damp weather, Check Engine Light on, loss of power and jerking, increased fuel consumption.

When your scan tool pulls code B1370, the vehicle's computer is telling you something specific: it has detected a short circuit to ground somewhere in the ignition tachometer signal circuit. This is not a vague sensor malfunction — it points directly to the wiring or components that carry the engine's RPM data back to the control module. The tach circuit feeds real-time engine speed information to the PCM, and when that signal gets grounded out, the module loses reliable rpm reading and sets B1370 to alert you.

The ignition tach circuit lives within the broader body electrical group under the OBD2 standard. Like all fault codes, B1370 does not trigger on a single bad reading. The control module requires the fault condition to persist across multiple drive cycles under specific conditions — load, temperature, rpm range — before it illuminates the Check Engine Light. When this code appears, the freeze frame data stored alongside it is your best starting point: it records the exact engine load, vehicle speed, coolant temperature, and RPM at the moment the module first saw the problem. Reproducing those conditions during your diagnosis is essential for confirming the failure.

This code is telling you the circuit is shorted to ground somewhere between the ignition coil or pickup and the PCM. The short could be in the wiring insulation, a connector, the coil itself, or even inside the engine control module. Water intrusion, oil contamination in spark plug wells, chafed wires from heat or movement, or a failed coil are the usual suspects. The fix is never guesswork — proper diagnosis narrows it down before you spend money on parts that might not be the problem.

Symptoms of B1370

• Check Engine Light stays on or flashes under acceleration
• Engine cranks slowly or fails to start, particularly in wet or humid conditions
• Noticeable loss of engine power and hesitation under load
• Rough idle or irregular misfiring at any rpm
• Fuel economy drops noticeably compared to normal driving history

Common Causes of B1370

• Damaged or corroded wiring harness and connectors in the ignition circuit
• Moisture or engine oil pooled in the spark plug tube wells, creating a conductive path to ground
• Failed ignition coil or ignition coil pack
• Worn, fouled, or incorrectly gapped spark plugs
• Faulty ignition control circuit internal to the ECM or PCM itself
• Poor electrical connections at the coil or crankshaft position sensor connector

How to Diagnose B1370

1. Hook up an OBD2 scanner and confirm B1370 is stored in the PCM. Record the associated freeze frame data — engine load, rpm, temperature, and speed recorded when the fault first occurred. You will need to recreate those exact conditions later to verify your repair.
2. Check for any related diagnostic trouble codes. Codes that appear alongside B1370 often point to the actual root cause, such as misfire codes or crankshaft position sensor faults. Also search manufacturer TSB databases by your vehicle make, model, and VIN — many B-series codes have documented factory fixes or software updates already identified.
3. Perform a thorough visual inspection of the ignition circuit wiring. Look for damaged insulation, wire chafing from rubbing against metal brackets or heat sources, corrosion at connectors, and loose or pushed-out pins. Pay special attention to the area around the coil and spark plug wells.
4. Test the ignition coil resistance with a multimeter against factory specifications, or swap the suspect coil with a known-good coil from another cylinder. If B1370 moves to a different cylinder with the swapped coil, the coil itself is faulty.
5. Remove and inspect the spark plugs. Check for oil fouling, carbon tracking on the ceramic, burned electrodes, and verify the gap matches the manufacturer's specification. Oil in the plug wells is a red flag — find the source and fix it before reinstalling.
6. Clear the code and complete a full drive cycle that reproduces the conditions from the freeze frame data. If B1370 does not return after the drive cycle and under the same load and temperature conditions, the repair is confirmed.

Repair Options and Costs

Depending on what your diagnosis uncovers, here are typical parts-and-labor costs at independent shop rates in USD:

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

Total Cost to Fix B1370

The final bill depends entirely on which part failed. Most straightforward repairs for B1370 fall in the $80–$380 range. The most expensive scenario — an ECM internal failure — is uncommon and should be ruled out last. Always confirm the exact fault with multimeter testing before replacing the engine computer, because diagnostic mistakes there are costly.

Can You Drive with B1370?

Drive with caution and limit heavy loads. An active ignition short circuit causes misfires, and sustained misfiring overheats the catalytic converter, potentially destroying it. If the Check Engine Light is flashing rather than steady, stop driving immediately and address the problem before it causes secondary damage.

Related OBD2 Codes

• B1300: Power Door Lock Circuit Failure
• B1301: Power Door Lock Circuit Open
• B1302: Accessory Delay Relay Coil Circuit Failure
• B1303: Accessory Delay Relay Coil Circuit Open
• B1304: Accessory Delay Relay Coil Circuit Short To Battery
• B1305: Accessory Delay Relay Coil Circuit Short To Ground