Glow Plug Circuit Low Input Bank #1 (Right)
The P1391 code indicates that the Engine Control Module (ECM) has detected a low voltage condition in the glow plug circuit for bank #1 (right side of the engine). This typically occurs in diesel engines where glow plugs are used to aid cold starts. The low input suggests a fault in the glow plug, wiring, or control module, leading to insufficient heating during startup.
1. Symptoms You Will Notice
- Hard starting, especially in cold weather
- Check Engine Light illuminated
- Rough idle or misfire during cold start
- Excessive white smoke from exhaust on startup
2. Most Common Causes
- Bank 2 oil control solenoid (OCV) stuck or failed in the advance position
- Bank 2 VCT actuator damaged or worn internally
- Bank 2 VCT actuator check valve defective
- Insufficient engine oil pressure or contaminated/degraded engine oil
- Bank 2 OCV oil filter screen clogged
- Bank 2 camshaft position (CMP) sensor signal erratic or out of phase
- Bank 2 timing chain stretched or tensioners faulty
- Bank 2 timing incorrectly set
3. Step-by-Step Diagnosis
Step 1: Scan the vehicle for codes and verify P1391 is present.
Step 2: Visually inspect glow plug wiring and connectors on bank #1 for damage or corrosion.
Step 3: Test glow plug resistance using a multimeter (should be low ohms).
Step 4: Check glow plug relay and fuse for proper operation.
Step 5: If all else is fine, replace the glow plug(s) in bank #1.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
It is not recommended to drive with this code, especially in cold weather, as it can cause hard starting and increased emissions. Continued driving may also damage the glow plug system or battery.
How much does it cost to fix?▼
The cost to fix P1391 typically ranges from $50 to $150, including parts (glow plugs) and labor. If the relay or wiring needs replacement, costs may be higher.
5. Commonly Affected Makes
This is a manufacturer-specific code. The exact manufacturer is not confirmed in our current database.