B1366: Ignition Start Circuit Short to Ground
The B1366 code indicates that the control module has detected a short to ground in the ignition start circuit. This circuit carries the start position signal from the ignition switch to various vehicle control modules. When a short to ground occurs, the signal voltage drops below the expected threshold, which can prevent the engine from starting or cause malfunctions in systems that rely on the ignition signal status.
1. Commonly Affected Makes
2. Most Common Causes
- Wiring or harness in the start circuit shorted to ground
- Defective or internally damaged ignition switch
- Corroded, oxidized, or bent pins in connectors along the circuit
- Internal failure in the control module (PCM, BCM, or GEM)
- Starter relay or associated components with insulation failure
3. Symptoms You Will Notice
- Engine fails to start or cranks but won't run
- No crank condition when turning the key to start
- Intermittent starting issues
- Other systems (e.g., security, accessories) may malfunction
4. Step-by-Step Diagnosis
Check for technical service bulletins (TSBs) related to the ignition start circuit.
Visually inspect the ignition switch wiring and connectors for damage, corrosion, or loose pins.
Test the ignition switch for proper operation and continuity in the start position.
Check for a short to ground in the start signal wire using a multimeter.
Inspect the starter relay and associated circuits for insulation breakdown.
If all else is normal, test the control module (PCM/BCM) for internal faults.
5. Frequently Asked Questions
Is it safe to drive?▼
No, this code indicates a high-severity issue that can prevent the engine from starting or cause unexpected stalling. It is not safe to drive the vehicle until the problem is diagnosed and repaired.
How much does it cost to fix?▼
Repair costs vary widely depending on the root cause. A simple wiring repair may cost $100-$200, while replacing an ignition switch can range from $150-$400. If the control module needs replacement, costs can exceed $1,000 including labor and programming.