P25B9 — Auxiliary Ignition Switch On/Start Position Circuit High

What Does P25B9 Mean?

P25B9 is a diagnostic trouble code indicating: Auxiliary Ignition Switch On/Start Position Circuit High. This code relates to the powertrain system. The vehicle's computer detected a condition outside normal operating parameters and stored this code.

Symptoms of P25B9

⚠️ Check Engine Light (MIL) illuminated
⚠️ Auxiliary Ignition Switch On/Start Position reading stuck at maximum value
⚠️ Related system operating erratically or in default mode
⚠️ Reduced engine performance

Common Causes

🔍 Short to voltage in Auxiliary Ignition Switch On/Start Position wiring harness
🔍 Corroded or water-damaged Auxiliary Ignition Switch On/Start Position connector
🔍 Faulty Auxiliary Ignition Switch On/Start Position outputting maximum voltage
🔍 Damaged wiring rubbing against metal components
🔍 ECM/PCM internal fault (rare)

Frequently Asked Questions

What does P25B9 mean?

P25B9 indicates: Auxiliary Ignition Switch On/Start Position Circuit High. 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 P25B9?

You can drive short distances for essential trips, but schedule a diagnosis soon. Driving with P25B9 for extended periods may cause additional problems.

How much does it cost to fix P25B9?

Repair costs for P25B9 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

🔧 Inspect and repair Auxiliary Ignition Switch On/Start Position wiring for short to voltage
🔧 Clean or replace corroded Auxiliary Ignition Switch On/Start Position connector
🔧 Replace faulty Auxiliary Ignition Switch On/Start Position

1
Find your vehicle above
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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.

P25B9: Auxiliary Ignition Switch On/Start Position Circuit High