P25B8 — Auxiliary Ignition Switch On/Start Position Circuit Low

What Does P25B8 Mean?

P25B8 is a diagnostic trouble code indicating: Auxiliary Ignition Switch On/Start Position Circuit Low. This code relates to the powertrain system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

Symptoms of P25B8

⚠️ Check Engine Light (MIL) illuminated
⚠️ Auxiliary Ignition Switch On/Start Position reading at zero or minimum value
⚠️ Related system not functioning or in fail-safe mode
⚠️ Reduced engine performance

Common Causes

🔍 Open or broken wire in Auxiliary Ignition Switch On/Start Position circuit
🔍 Poor ground connection at Auxiliary Ignition Switch On/Start Position
🔍 Faulty Auxiliary Ignition Switch On/Start Position with no output signal
🔍 Disconnected or loose Auxiliary Ignition Switch On/Start Position connector
🔍 Blown fuse in related circuit

Frequently Asked Questions

What does P25B8 mean?

P25B8 indicates: Auxiliary Ignition Switch On/Start Position Circuit Low. The vehicle's computer has detected that the Auxiliary Ignition Switch On/Start Position is not operating within its expected parameters and stored this diagnostic trouble code.

Can I drive with code P25B8?

You can drive short distances for essential trips, but schedule a diagnosis soon. Driving with P25B8 for extended periods may cause additional problems.

How much does it cost to fix P25B8?

Repair costs for P25B8 typically range from $20 to $300, depending on the root cause. Simple wiring or connector repairs are on the lower end, while component replacement costs more. A proper diagnosis ($80–$150 at most shops) will identify the exact cause before committing to expensive parts.

What To Do Next

Possible Fixes

🔧 Repair broken wire or restore ground in Auxiliary Ignition Switch On/Start Position circuit
🔧 Clean and secure Auxiliary Ignition Switch On/Start Position connector and ground points
🔧 Replace failed Auxiliary Ignition Switch On/Start Position

1
Find your vehicle above
Click your make and model for real owner reports and common causes specific to your vehicle.
2
Check for recalls
Go to nhtsa.gov/recalls and enter your VIN. Free repairs if covered.
3
Get a professional diagnosis
A code alone doesn't identify the exact failed part. A diagnostic ($50–$150) pinpoints the root cause.

P25B8: Auxiliary Ignition Switch On/Start Position Circuit Low