Test Dc - Mass Airflow Sensor (MAF)

NOTE: Perform this test when Code 26, 56, or 66 is displayed in the QUICK TESTS or when directed here by test charts. This test procedure is intended to diagnose only the MAF, ECA and vehicle harness circuits (VPWR, PWR GND, MAF and MAF RTN).

NOTE: To prevent replacement of good components, be aware that the following non-EEC related areas may be at fault:

Air cleaner element
Inlet air duct
Throttle body

Fig 1: Mass Airflow Sensor (MAF) Circuits

MAF SENSOR TEST PIN ID

Test Pin No.	Wire Color
Pin 9 or 15	Tan/Light Blue
Pin 14 or 50	Dark Blue/Orange
Pin 37 or 57	Red
Pin 40 or 60	Black/Light Green

MAF SIGNAL VOLTAGE

Application	Volts
Idle	.60
20 MPH	1.10
40 MPH	1.70
60 MPH	2.10

NOTE: MAF signal voltage is typical for an A/T equipped vehicle at normal operating temperature. Voltage signal may vary due to engine load and temperature.

1) Code 26: Check VPWR Circuit Voltage Code 26 indicates MAF sensor voltage is out of Self-Test. If code was received during KOEO Self-Test, voltage exceeded .70 volt test range. If Code 26 was received during KOER Self-Test, voltage was not within .20 to 1.50 volt operating range. Possible causes for this fault are a faulty MAF sensor or ECA.

NOTE: Code 26 may be caused by use of a garage exhaust ventilation system. Ensure vehicle is vented to outside atmosphere before repeating QUICK TEST.

Turn key off and disconnect MAF sensor. Set DVOM on 20-volt scale. Turn key on, leaving engine off. Measure voltage between VPWR circuit at the MAF sensor vehicle harness connector and the battery negative post. If voltage is greater than 10.5 volts, go to next step. If not, reconnect MAF sensor and go to TEST B, step 1).

2) Check MAF Sensor Ground With KOEO and MAF sensor disconnected, set DVOM on 20-volt scale. Measure voltage between VPWR circuit and PWR GND circuit at the MAF sensor connector. If voltage is greater than 10.5 volts, go to next step. If voltage is less than 10.5 volts repair open PWR GND circuit, reconnect MAF and rerun QUICK TEST.

NOTE: There is a break in the step numbering sequence at this point, skipping from step 2) to step 10). Break is due to previous chart references to these testing procedures. No test procedures have been omitted.

10) Code 66: Check Continuity of MAF Signal & VPWR Circuits Code 66 indicates that MAF signal was less than .40 volt during engine continuous operation or during KOER Self-Test. Possible causes for this fault are:

Open MAF circuit
Open VPWR circuit to MAF sensor
Open PWR GND circuit to MAF sensor
MAF circuit shorted to ground
Faulty ECA or MAF sensor
Air leak before or after MAF sensor
MAF sensor disconnected

Ensure key is off. Disconnect and inspect 60-pin connector at ECA. Repair and service as necessary. Disconnect the MAF sensor and install breakout box, leaving ECA disconnected. Set DVOM on 200-ohm scale. Measure resistance between VPWR circuit at the MAF sensor vehicle harness connector and test pins No. 37 and 57 at the breakout box. Measure resistance between MAF circuit at MAF sensor vehicle harness connector and test pin No. 50 at breakout box. If both resistances are less than 5 ohms, go to next step. If either resistance is greater than 5 ohms, remove breakout box, repair open circuit, reconnect all components and rerun QUICK TEST.

11) Check MAF Ckt For Shorts to Ground & MAF RTN Ckt With key off and MAF sensor disconnected, set DVOM on 200-k/ohm scale. Disconnect ECA 60-pin connector, inspect connector and terminals. Install breakout box leaving ECA disconnected. Measure resistance between test pin No. 50 and test pins No. 9, 40, and 60, at the breakout box. If all resistances are greater than 10 k/ohms, go to next step. If resistance in any circuit is less than 10 k/ohms, repair short circuit, remove breakout box, reconnect components and repeat QUICK TEST.

12) Check Continuity of PWR GND Circuit Ensure key is turned off and disconnect MAF sensor. Set DVOM on 200-ohm scale. Measure resistance between PWR GND circuit at MAF sensor vehicle harness connector and battery negative post. If resistance is less than 5 ohms, go to next step. If resistance is greater than 5 ohms, repair open circuit, reconnect all components and repeat QUICK TEST. If resistance is 5 ohms or less, go to next step.

13) Check Continuity of MAF RTN Circuit With key off and MAF sensor disconnected, set DVOM on 200-ohm scale. Disconnect ECA 60-pin connector, inspect pins and install breakout box, leave ECA disconnected. Measure resistance between MAF RTN circuit at the MAF sensor vehicle harness connector, and test pin No. 9 at the breakout box.

If resistance is less than 5 ohms, go to next step. If resistance is more than 5 ohms, remove breakout box, reconnect components and repeat QUICK TEST.

14) Check MAF Signal For Short to Ground With key off, breakout box installed, and ECA connected, disconnect MAF sensor. Set DVOM on 200-k/ohm scale. Measure resistance between test pin No. 50 and test pins No. 9, 40, and 60 at the breakout box. If all resistances are less than 10 k/ohms, remove breakout box. Replace ECA, remove breakout box, reconnect components and repeat QUICK TEST. If resistances are greater than 10 k/ohms, go to next step.

15) Check MAF Circuit Output With key off, install breakout box. Ensure ECA and MAF are connected. Set DVOM on 20-volt scale. Start engine. Measure voltage between test pin No. 50 at the breakout box and battery negative post. If voltage is between .2 and 1.5 volts replace ECA, remove breakout box, reconnect components and repeat QUICK TEST. If voltage is not between .2 and 1.5 volts, replace MAF sensor, remove breakout box, reconnect components and repeat QUICK TEST.

NOTE: There is a break in the step numbering sequence at this point, skipping from step 15) to step 20). Break is due to previous chart references to these testing procedures. No test procedures have been omitted.

20) Code 56: Repeat Self-Test With MAF Sensor Disconnected With key off, disconnect MAF sensor from vehicle harness. Start engine and allow to idle for one minute. Turn key off. Repeat KOEO Self-Test. If Code 66 is present, replace MAF sensor and rerun QUICK TEST. If Code 66 is not present, go to next step.

21) Check MAF Circuit For Short to VPWR With key off, install the breakout box and disconnect MAF sensor and ECA. Disconnect ECA 60-pin connector, inspect for damaged or corroded terminals and repair as necessary. Set DVOM on 200-k/ohm scale. Measure resistance between MAF circuit and VPWR circuit at the MAF sensor vehicle harness connector. If resistance is greater than 10 k/ohms, replace ECA, remove breakout box, reconnect components and repeat QUICK TEST. If resistance is less than 10 k/ohms, repair circuit short, remove breakout box, reconnect components and repeat QUICK TEST.