OBD2 Code B1370: Tachometer Signal Short to Ground
The B1370 code indicates that the Body Control Module (BCM) or instrument cluster has detected a short to ground in the tachometer signal circuit from the engine control module (ECM/PCM). This circuit carries the engine RPM signal to the instrument cluster for tachometer display. A short to ground prevents the signal from reaching the cluster, causing the tachometer to stop working or display erratic readings. In GM vehicles, this is typically a 5V or 12V pulse signal monitored by the BCM or IPC.
1. Commonly Affected Makes
2. Most Common Causes
- Short to ground in the tachometer signal wiring
- Damaged wiring harness near the engine or steering column
- Faulty instrument cluster (IPC) or BCM
- Corroded or damaged pins in the instrument cluster connector
- Faulty ECM/PCM generating an incorrect or overloaded signal
- Aftermarket electrical modifications (alarms, accessories) interfering with the circuit
3. Symptoms You Will Notice
- Tachometer not working or reading zero
- Erratic or fluctuating tachometer readings
4. Step-by-Step Diagnosis
Check for technical service bulletins (TSBs) related to B1370 for the specific vehicle.
Visually inspect the tachometer signal wiring for shorts, damage, or corrosion, especially near the engine and steering column.
Test the tachometer signal circuit for continuity to ground using a multimeter.
Inspect the instrument cluster connector for bent, corroded, or damaged pins.
If wiring and connectors are okay, test the ECM/PCM output signal with a scope or multimeter.
If the signal is present at the ECM but not at the cluster, repair the open or short in the wiring.
If the signal is missing at the ECM, diagnose the ECM/PCM for internal failure.
5. Frequently Asked Questions
Is it safe to drive?▼
Yes, it is generally safe to drive short distances, but you will not have a functioning tachometer, which may make it difficult to monitor engine RPM. The underlying electrical issue should be repaired promptly to avoid potential damage to other modules.
How much does it cost to fix?▼
The cost can range from $100 to $400 depending on the cause. Simple wiring repairs may cost $100-$200, while replacing a faulty instrument cluster or BCM can cost $300-$400 or more, including labor.