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GTECH Calibration
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P1202

(AlternativeFuel) Gas Mass Sensor Circuit Low Frequency.

  • Buick
  • Powertrain
  • Manufacturer code
  • Medium severity

How this code is built

P
SystemPowertrain
1
Defined byThe manufacturer
2
AreaFuel and air metering (injector circuit)
02
FaultThe specific fault in that area

What it means

On a Buick, P1202 means the engine control module has detected that the signal from the alternative fuel gas mass sensor (used on bi-fuel or dedicated gaseous fuel setups such as natural gas or LPG) is at a lower frequency than expected. The module monitors the sensor's frequency output and sets the code when it falls below the calibrated range. This points to a problem with the sensor, its wiring or its supply, or with the gas fuel system it is measuring.

Symptoms

  • Malfunction indicator lamp on
  • Poor running or hesitation when operating on gas fuel
  • Car switching to petrol only, or refusing to run on gas
  • Rough idle or poor fuel metering on gas
  • Reduced power or range on gas

Possible causes

  • Faulty alternative fuel gas mass sensor giving a low frequency outputlikely
  • Damaged, corroded or loose wiring or connector at the sensor (open circuit, high resistance or short to ground)likely
  • Poor or missing sensor power supply or groundpossible
  • Blocked, restricted or contaminated gas supply affecting sensor readingspossible
  • Fault in the gas fuel system such as pressure regulation or low gas supplypossible
  • Faulty engine control module or its sensor input circuitrare

How to diagnose

  1. Read all stored and pending codes and note the freeze frame data, including which fuel the engine was running on at the time
  2. Check that the gas tank has fuel and that supply valves are open, as a low gas supply can mimic a sensor fault
  3. Visually inspect the sensor, its harness and connector for damage, corrosion, water ingress, chafing or heat damage
  4. Check the sensor power supply and ground at the connector against the manufacturer's wiring information
  5. Check the sensor signal with a scope or meter and compare the frequency with the specified value at the relevant operating conditions
  6. Check the gas fuel system for pressure, restrictions or leaks, following the manufacturer's procedure for this model and fuel type
  7. Wiggle-test the harness while watching the sensor signal to find intermittent faults
  8. If the sensor, wiring and supply all prove good, check the module's input and look for any applicable calibration update

How to fix

  • Repair or replace damaged wiring, terminals or connectors in the sensor circuit
  • Replace the alternative fuel gas mass sensor if its output is out of specification
  • Restore the correct power or ground supply to the sensor
  • Correct gas fuel supply or pressure faults found during testing
  • Replace or reprogram the engine control module only if confirmed faulty, or if an applicable updated calibration is known to address the fault

Can I keep driving?

Medium severity

The car can usually still be driven, often on petrol, but gas operation may be poor and the fault should be fixed soon. Avoid prolonged driving on gas if it is running badly, and stop if you smell gas or notice any leak.

Guide written by AI from the code's definition. Confirm with a diagnosis before replacing parts.

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