P1748 — Transmission Control Module Self Test

What Does P1748 Mean?

P1748 is a manufacturer-specific diagnostic trouble code: Transmission Control Module Self Test. This code applies to BMW, VOLKSWAGEN, MAZDA, JAGUAR, FORD 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 P1748

⚠️ Check Engine Light (MIL) illuminated
⚠️ Transmission Control Module Self Test not functioning as expected
⚠️ Related system may be in fail-safe mode
⚠️ Reduced engine performance

Common Causes

🔍 Faulty Transmission Control Module Self Test
🔍 Wiring or connector issue in Transmission Control Module Self Test circuit
🔍 Related mechanical or electrical fault
🔍 ECM/PCM issue (rare)

Frequently Asked Questions

What does P1748 mean?

P1748 indicates: Transmission Control Module Self Test. The vehicle's computer has detected that the Transmission Control Module Self Test is not operating within its expected parameters and stored this diagnostic trouble code.

Can I drive with code P1748?

You can drive short distances for essential trips, but schedule a diagnosis soon. Driving with P1748 for extended periods may cause additional problems.

How much does it cost to fix P1748?

Repair costs for P1748 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 Transmission Control Module Self Test and related wiring
🔧 Replace faulty Transmission Control Module Self Test

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.

P1748: Transmission Control Module Self Test