P1812 — Transmission 4-Wheel Drive Mode Select Circuit Failure

What Does P1812 Mean?

P1812 is a manufacturer-specific diagnostic trouble code: Transmission 4-Wheel Drive Mode Select Circuit Failure. This code applies to FORD, LINCOLN, MERCURY, OTHER, BUICK vehicles. Unlike generic OBD-II codes, manufacturer-specific codes are defined by the vehicle maker and may only apply to certain makes and models.

Symptoms of P1812

⚠️ Check Engine Light (MIL) illuminated
⚠️ Erratic Transmission 4-Wheel Drive Mode Select readings
⚠️ Related system operating intermittently
⚠️ Reduced engine performance

Common Causes

🔍 Wiring issue in Transmission 4-Wheel Drive Mode Select circuit (damaged, chafed, or corroded)
🔍 Faulty Transmission 4-Wheel Drive Mode Select connector or terminal
🔍 Failed Transmission 4-Wheel Drive Mode Select
🔍 ECM/PCM connection issue

Frequently Asked Questions

What does P1812 mean?

P1812 indicates: Transmission 4-Wheel Drive Mode Select Circuit Failure. The vehicle's computer has detected that the Transmission 4-Wheel Drive Mode Select is not operating within its expected parameters and stored this diagnostic trouble code.

Can I drive with code P1812?

You can drive short distances for essential trips, but schedule a diagnosis soon. Driving with P1812 for extended periods may cause additional problems.

How much does it cost to fix P1812?

Repair costs for P1812 typically range from $80 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 Transmission 4-Wheel Drive Mode Select wiring and connectors
🔧 Replace faulty Transmission 4-Wheel Drive Mode Select

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.

P1812: Transmission 4-Wheel Drive Mode Select Circuit Failure