Fuel and air

P0104 — Mass Air Flow (MAF) Sensor Circuit "A" Intermittent/Erratic

Severity: medium Drive with care, to a shop

What P0104 means

The engine control unit uses the mass air flow sensor to measure how much air enters the engine and to calculate how much fuel to inject. P0104 sets when that signal jumps around, drops out or doesn't match what the ECU expects for the engine load and speed. As a result, the air-fuel mixture can't be calculated accurately.

Symptoms

  • Check Engine light on
  • Rough or unstable idle
  • Hesitation or stumbling when accelerating
  • Reduced power and worse fuel economy
  • Intermittent stalling or hard starting
  • Occasional black exhaust smoke
  • Abnormal fuel trim values

Possible causes

  1. Dirty or contaminated MAF sensing element
  2. Failing MAF sensor
  3. Damaged wiring, corroded connector pins or poor ground in the MAF circuit
  4. Unmetered air leaking in after the sensor (ducting, boot, clamps)
  5. Moisture or oil on the sensor, for example from an over-oiled air filter
  6. Rarely, a fault in the ECU input circuit

How to diagnose

  1. Read the codes and freeze frame data to see when the fault set
  2. Inspect the MAF connector for a loose lock, corrosion or moisture
  3. Wiggle the harness with the engine running while watching the MAF reading on a scan tool
  4. Test power, ground and reference voltage at the sensor connector with a multimeter
  5. Inspect the intake duct between the MAF and throttle body for cracks and loose clamps
  6. Compare air flow readings at idle and under load with expected values for the engine
  7. Check short-term and long-term fuel trims
  8. Check the air filter and the sensor element for dirt or oil

Common fixes

  • Clean the MAF sensor with a dedicated MAF cleaner
  • Repair the wiring or replace a damaged connector
  • Fix the air leak by replacing the duct or tightening clamps
  • Replace the MAF sensor with an OEM or quality equivalent
  • Replace the air filter if it is dirty or oil-soaked

Questions and answers

Can I drive with a P0104 code?

For a short time, yes, but the engine may stall or lose power unexpectedly. Don't put off diagnosis, especially if you notice stumbling or hesitation.

Will cleaning the MAF sensor fix P0104?

Sometimes, if contamination is the cause. If the code returns, check the connector, wiring and intake air leaks, then consider replacing the sensor.

Can I just clear the P0104 code?

Clearing it only turns the light off for a while. Until the cause is fixed the code will come back and the engine will keep running on an inaccurate mixture.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.