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P1202

Alternative Fuel Gas Mass Sensor Circuit Low Frequency.

  • Oldsmobile
  • 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 Oldsmobile (GM) models fitted with a gas-fuelled system, P1202 means the engine control module saw the gas mass sensor signal frequency below the expected range. The module reads this sensor to work out how much alternative fuel gas is flowing to the engine, so a low frequency suggests a sensor, wiring or supply problem. Whether a given Oldsmobile model uses this sensor depends on the engine and fuel system, so confirm the fitment before diagnosing.

Symptoms

  • Malfunction indicator lamp on
  • Poor running or hesitation on gas fuel
  • Rough idle or stalling
  • Reduced power or poor fuel economy
  • Hard starting on gas or the system defaulting to petrol

Possible causes

  • Damaged wiring or poor connector contact in the gas mass sensor signal, supply or earth circuitlikely
  • Faulty gas mass sensor giving a low-frequency outputlikely
  • Low or restricted gas supply, such as a nearly empty tank, blocked filter or faulty regulatorpossible
  • Poor power or earth supply to the sensor from a fuse, relay or earth pointpossible
  • Gas leak or air leak in the supply pipework near the sensorpossible
  • Fault inside the engine control module or its software calibrationrare

How to diagnose

  1. Read all stored and pending codes and note the freeze frame data, including fuel type in use and engine load
  2. Check the gas tank contents and look for other fuel system codes that point to supply problems
  3. Visually inspect the sensor harness and connector for chafing, corrosion, bent pins, heat damage and moisture
  4. Check the sensor's supply voltage and earth with a multimeter against the manufacturer's specification
  5. Check the sensor signal with a scope or frequency-capable meter, comparing it with specification at idle and under raised engine speed
  6. Inspect the gas pipework, filter and regulator for leaks, restriction and correct pressure, following gas system safety procedures
  7. Check for any applicable software updates or technical bulletins for the specific model and engine
  8. Clear the code and road test to see whether it returns

How to fix

  • Repair or replace damaged wiring and clean or replace corroded connectors
  • Replace the gas mass sensor if its output is out of specification
  • Correct supply problems by refilling, or by replacing a blocked filter or faulty regulator
  • Restore the sensor's power and earth supply by repairing fuses, relays or earth points
  • Repair any gas or air leaks in the supply pipework, using a qualified gas system specialist
  • Update or replace the control module software or unit only if testing confirms it is faulty or outdated

Can I keep driving?

Medium severity

The car can usually be driven for a short time, often on petrol if it is a dual-fuel setup, but get it checked soon. Stop driving and seek help if you smell gas or the engine runs very badly.

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

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