P1203 — (Alternative Fuel) Gas Mass Sensor Circuit High Frequency

What Does P1203 Mean?

P1203 is a manufacturer-specific diagnostic trouble code: (Alternative Fuel) Gas Mass Sensor Circuit High Frequency. This code applies to BUICK, CADILLAC, CHEVY, CHRYSLER, GM 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 P1203

⚠️ Check Engine Light (MIL) illuminated
⚠️ (Alternative Fuel) Gas Mass Sensor reading stuck at maximum value
⚠️ Related system operating erratically or in default mode
⚠️ Reduced engine performance

Common Causes

🔍 Short to voltage in (Alternative Fuel) Gas Mass Sensor wiring harness
🔍 Corroded or water-damaged (Alternative Fuel) Gas Mass Sensor connector
🔍 Faulty (Alternative Fuel) Gas Mass Sensor outputting maximum voltage
🔍 Damaged wiring rubbing against metal components
🔍 ECM/PCM internal fault (rare)

Frequently Asked Questions

What does P1203 mean?

P1203 indicates: (Alternative Fuel) Gas Mass Sensor Circuit High Frequency. The vehicle's computer has detected that the (Alternative Fuel) Gas Mass Sensor is not operating within its expected parameters and stored this diagnostic trouble code.

Can I drive with code P1203?

You can drive short distances for essential trips, but schedule a diagnosis soon. Driving with P1203 for extended periods may cause additional problems.

How much does it cost to fix P1203?

Repair costs for P1203 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 (Alternative Fuel) Gas Mass Sensor wiring for short to voltage
🔧 Clean or replace corroded (Alternative Fuel) Gas Mass Sensor connector
🔧 Replace faulty (Alternative Fuel) Gas Mass Sensor

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.

P1203: (Alternative Fuel) Gas Mass Sensor Circuit High Frequency