DTC 1-2-1

1-2-1 MASS AIR FLOW SENSOR SIGNAL

Condition(s) for DTC
^ Since the computed mass air flow is determined largely by the injection period, the system is dependent on the Mass Air Flow (MAF) Sensor signal. The DTC is recorded if the control module detects that the signal is lower than 2.7 Volts or higher than 8 Volts.

Substitute value
^ The control module assumes a fixed load signal value (limp home) when the DTC is recorded. The adaptive and idling control functions are inhibited, and the Ignition Control Module (ICM) and AW 50-42 Transmission Control Module (TCM) load signal is adjusted to the full-load value.

Fault source(s)
^ Open-circuit in signal or supply lead.
^ Signal lead short-circuited to ground or supply.
^ Contact resistance in connections.
^ MAF sensor faulty.

Fault symptom(s)
^ None.

TESTING PROCEDURE





Other DTCs
^ Read other DTCs.

If MFI DTC 2-2-3 is recorded:
- Check lead between Idle Air Control (IAC) valve terminal 3 and MFI control module A16, and between IAC valve terminal 1 and MFI control module A17 for short-circuit to supply.
If MFI DTC 2-2-3 is not recorded:
- Check status message.





Check Status Message
^ Check current Status Message..

If Status message is: Permanent fault, faulty signal.
- Proceed to: PERMANENT FAULT, FAULTY SIGNAL section below.
If Status message is: Intermittent fault, faulty signal.
- Proceed to: INTERMITTENT FAULT, FAULTY SIGNAL section below.

PERMANENT FAULT, FAULTY SIGNAL





Checking MAF sensor supply voltage
^ Switch ON ignition.
^ Disconnect MAF sensor connector.
^ Connect voltmeter between MAF sensor connector terminal 3 and ground.

Instrument should indicate battery voltage.

If reading is correct:
- Check power ground.
If reading is incorrect:
- Check lead between MAF sensor connector terminal 3 and main relay (2/32) terminal 3 for open-circuit.





Checking power ground
^ Switch OFF ignition.
^ Disconnect MAF sensor.
^ Connect ohmmeter between MAF sensor connector terminal 2 and ground.

Instrument should indicate approx. 0 Ohms.

If reading is correct:
- Check signal ground.
If reading is incorrect:
- Check lead between MFI module A8 and MAF sensor connector terminal 2 for open-circuit.





Checking signal ground
^ Switch OFF ignition.
^ Disconnect MAF sensor.
^ Connect ohmmeter between MAF sensor connector terminal 1 and ground.

Instrument should indicate 500 - 1500 Ohms.

If reading is correct:
- Check MAF sensor connector.
If reading is incorrect:
- Check lead between MFI module A12 and MAF sensor connector terminal 1 for open-circuit.





Checking MAF sensor connector
^ Switch OFF ignition.
^ Connect test box to MFI system and check ground terminals.
^ Connect module.
^ Connect MAF sensor.





^ Switch ON ignition.
^ Connect voltmeter across #13 (MFI A13) and #20 (MFI A20) on test box.

Instrument should indicate approx. 2.8 Volts.

If reading is correct:
- DTC is due to poor connection in MAF sensor and control module connector. Check connectors for contact resistance and oxidation.
If reading is approx. 0 Volts:
- Check resistance of MAF sensor signal lead.
If reading indicates battery voltage:
- Check voltage in signal lead.





Checking resistance of MAF sensor signal lead
^ Switch OFF ignition.
^ Disconnect MAF sensor.
^ Connect ohmmeter between MAF sensor connector terminal 4 and ground.

Instrument should indicate approx. 25K Ohms.

If reading is correct:
- Try with new MAF sensor.
If instrument indicates approx. 0 Ohms:
- Check lead between MFI module A13 and MAF sensor connector terminal 4 for short-circuit to ground.
If instrument indicates infinity (no continuity):
- Check lead between MFI module A13 and MAF sensor connector terminal 4 for open-circuit.





Checking voltage in signal lead
^ Switch ON ignition.
^ Disconnect MAF sensor.
^ Connect voltmeter between MAF sensor connector terminal 4 and ground.

Instrument should indicate approx. 0 Volts.

If reading is correct:
- Try with new MAF sensor.
If reading is incorrect:
- Check lead between MFl module #13 and MAF sensor connector terminal 4 for short-circuit to supply.

INTERMITTENT FAULT, FAULTY SIGNAL





Checking wiring and connections
^ Check MAF sensor and ICM connectors for loose connections, and for contact resistance and oxidation.
^ Check lead between ICM A13 and MAF sensor connector terminal 4 for intermittent open-circuit, intermittent short-circuit to ground and intermittent short-circuit to supply.
^ Check lead between MAF sensor connector terminal 3 and main relay (2/32) terminal 3 for intermittent open-circuit.
^ Check lead between MFI module A8 and MAF sensor connector terminal 2 for intermittent open-circuit.
^ Check lead between MFI module A12 and MAF sensor connector terminal 1 for intermittent open-circuit.