DTC 1-2-1
1-2-1 MASS AIR FLOW SENSOR SIGNALPreconditions for DTCs
^ If the signal from the Mass Air Flow (MAF) Sensor is lower than 0.2 Volts or greater than 2.2 Volts at idling speed, or is considered unsatisfactory according to RPM and throttle angle, this is interpreted by the control module as a fault and DTC 1-2-1 is set.
Substitute values
^ The control module uses engine speed and throttle angle to determine the load.
^ The Idle Air Control (IAC) valve's idle air trim is inhibited.
^ Long term fuel trim inhibited.
^ Only initial charge pressure is permitted.
^ The EVAP diagnosis is inhibited.
Fault sources
^ Signal too high:
- Signal lead short circuited to voltage supply.
- Break in lead to signal or power ground.
- Defective MAF sensor.
- Contact resistance in connections.
^ Signal too low:
- Break in signal or voltage lead.
- Signal lead short circuited to ground.
- Damaged or loose fresh-air hose, upper charge air cooler pipe or lower charge air cooler pipe.
- Defective MAF sensor.
- Contact resistance in connections.
Fault symptoms
^ Uneven idling and/or jerky operation.
^ Poorer performance from initial charge pressure limit.
TESTING PROCEDURE
Status Message
^ Check current status message.
If Status message is: Permanent fault, signal too high:
- Proceed to: PERMANENT FAULT, SIGNAL TOO HIGH section below.
If Status message is: Permanent fault, signal too low:
- Proceed to: PERMANENT FAULT, SIGNAL TOO LOW section below.
If Status message is: Intermittent fault, signal too high:
- Proceed to: INTERMITTENT FAULT, SIGNAL TOO HIGH section below.
If Status message is: Intermittent fault, signal too low:
- Proceed to: INTERMITTENT FAULT, SIGNAL TOO LOW section below.
PERMANENT FAULT, SIGNAL TOO HIGH
Checking Power Ground
^ Switch Ignition OFF.
^ Wait for about 150 seconds.
^ Disconnect MAF sensor.
^ Connect an ohmmeter between the MAF sensor's connector 1 and ground.
The ohmmeter should show approx. 0 ohms.
If reading is OK:
- Check signal ground.
If reading is incorrect:
- Check the ECM's connector.
Checking the ECM's Connector
^ Switch Ignition OFF.
^ MAF sensor disconnected.
^ Rectify the ECM's connector with regard to contact resistance an oxidation.
^ ECM connected.
^ Connect an ohmmeter between the MAF sensor's connector 1 and ground.
The ohmmeter should show approx. 0 ohms.
If reading is OK:
- Check signal ground.
If reading is incorrect:
- Check the lead between the MAF sensor connector 1 and ECM A3 for signs of a break.
Checking Signal Ground
^ Switch Ignition OFF.
^ The MAF sensor is disconnected.
^ Connect an ohmmeter between the MAF sensor's connector 2 and ground.
The ohmmeter should show approx. 0 ohms.
If the reading is OK:
- Check the signal lead.
If reading is incorrect:
- Check the ECM's connector.
Checking the ECM's Connector
^ Switch Ignition OFF.
^ MAF sensor disconnected.
^ Rectify the ECM's connector with regard to contact resistance and oxidation.
^ ECM connected.
^ Connect an ohmmeter between the MAF sensor's connector 2 and ground.
The ohmmeter should show approx. 0 ohms.
If the reading is OK:
- Check the signal lead.
It the reading is incorrect:
- Check the lead between the MAF connector 2 and ECM A5 for signs of a break.
Checking the Signal Lead
^ Switch Ignition ON.
^ MAF sensor disconnected.
^ Connect a voltmeter between the MAF sensor's connector 4 and ground.
The voltmeter should show 0 - 1 Volts.
If reading is OK:
- Check the MAF signal.
If reading is incorrect:
- Check the lead between MAF sensor connector 4 and ECM A4 for signs of short circuiting to voltage.
After remedying: Check the MAF sensor.
Checking the MAF Signal
^ Switch Ignition OFF.
^ Connect the MAF sensor.
^ Switch Ignition ON.
^ Connect a voltmeter between MAF sensor's connectors 2 and 4.
The voltmeter should show 0.1 - 0.2 Volts.
If the reading is OK:
- The source of the DTC is poor contact in the MAF sensor's and/or ECM's connector. Rectify the connection with regard to contact resistance and oxidation.
If reading is incorrect:
- Test with a new MAF sensor.
Checking the MAF Sensor
^ The MAF sensor may break as a sequential fault resulting from short circuiting of the signal lead to voltage. Check the MAF sensor as below.
^ Switch Ignition OFF.
^ Connect the MAF sensor.
^ Switch Ignition ON.
^ Connect a voltmeter between the MAF sensor's connectors 2 and 4.
The voltmeter shows 0.1 - 0.2 Volts.
If the reading is OK:
- The MAF sensor is OK.
If reading is incorrect:
- Test with a new MAF sensor.
PERMANENT FAULT, SIGNAL TOO LOW
Checking the Fresh Air Hose, Upper And Lower Charge Air Pipes
^ Switch Ignition OFF.
^ Check that the fresh air hose and the upper and lower charge air pipes are undamaged and that they are securely connected to their couplings.
If the hose and pipes are OK:
- Check the voltage lead.
If the hose and pipes are NOT OK:
- Rectify as necessary.
Checking the Voltage Lead
^ Switch Ignition OFF.
^ Disconnect the MAF sensor.
^ Switch Ignition ON.
^ Connect a voltmeter between the MAF sensor's connector 3 and ground.
The voltmeter should show battery voltage.
If reading is OK:
- Check the signal lead.
If reading is incorrect:
- Check the lead between the MAF sensor's connector 3 and the main relay (2/32) connector 3 for signs of a break.
Checking the Signal Lead
^ Switch Ignition OFF.
^ Wait for about 150 seconds.
^ MAF sensor disconnected.
^ Connect an ohmmeter between the MAF sensor's connector 4 and ground.
The ohmmeter should show approx. 9 - 11K ohms.
If reading is OK:
- See Checking the MAF sensor signal below.
If the ohmmeter shows approx. 0 ohms:
- Check the lead between the MAF sensor's connector 4 and ECM A4 for signs of short circuiting to ground.
If the ohmmeter shows infinite resistance:
- Check the lead between the MAF sensor's connector 4 and ECM A4 for signs of a break.
Checking the MAF Sensor's Signal
^ Switch Ignition OFF.
^ Connect the MAF sensor.
^ Switch Ignition ON.
^ Connect a voltmeter between the MAF sensor's connectors 4 and 2.
The voltmeter should show approx. 0.1 - 0.2 Volts.
If reading is OK:
- The source of the DTC is poor contact in the MAF sensor's and/or ECM's connector. Rectify the connectors with regard to contact resistance and oxidation.
If reading is incorrect:
- Test with a new MAF sensor.
INTERMITTENT FAULT, SIGNAL TOO HIGH
Checking the Leads And Connections
^ Check the MAF sensor's and control modules connectors for signs of loose contact and contact resistance and oxidation.
^ Check the lead between the MAF sensor's connector 1 and ECM A3 for signs of an intermittent break.
^ Check the lead between the MAF sensor's connector 2 and ECM A5 for signs of an intermittent break.
^ Check the lead between the MAF sensor's connector 4 and ECM A4 for signs of intermittent short circuiting to voltage supply, intermittent short circuiting to ground and intermittent breaks.
^ Check the lead between the main relay (2/32) connector 4 and MAF connector 3 for signs of intermittent break.
^ Check that the fresh air hose, upper and lower intercooler pipes are undamaged and that they are securely connected to their couplings.
INTERMITTENT FAULT, SIGNAL TOO LOW
Checking the Leads And Connections
^ Check that the fresh air hose, upper and lower charge air cooler pipes are undamaged and properly attached to their couplings.
^ Check the lead between the main relay (2/32) connector 3 and MAF sensor connector 3 for signs of an intermittent break.
^ Check the lead between the MAF sensor's connector 4 and ECM A4 for signs of an intermittent break and intermittent short circuiting to ground.