Diagnostic Aids

Perform this test when directed by QUICK TEST. This test procedure is only intended to diagnose MAF sensor, ECA and wiring harness circuits (VPWR, PWR GND, MAF and MAF RTN).

To prevent replacement of good components, be aware following non-EEC related areas may be cause of problem:

Air cleaner element.
Inlet air duct.
Throttle body.

Code 26/159, retrieved during KOEO SELF-TEST, indicates voltage exceeded .7-volt test range. Code 26/159, retrieved during KOER SELF-TEST, indicates voltage is not within .2-1.5 volts operating range. Possible causes are faulty MAF sensor or ECA.

Fig 1: Mass Airflow (MAF) Sensor Ckts. & Connector Terminal ID

TEST PIN NO. 14 OR 50 (MAF) WIRE COLOR ID

Application	Wire Color
Escort 1.9L & Tracer 1.9L	Brown/Black
Mustang 2.3L, 3.8L RWD Cougar 5.0L & Thunderbird 5.0L	Dark Blue/Orange
All Other Models	Light Blue/Red

TEST PIN NO. 9 OR 15 (MAF RTN) WIRE COLOR ID

Application	Wire Color
Escort 1.9L & Tracer 1.9L	Gray/Yellow
Except Escort 1.9L & Tracer 1.9L	Tan/Light Blue

TEST PINS NO. 37 & 57 (VPWR) WIRE COLOR ID

Application	Wire Color
Except Probe 3.0L	Red
Probe 3.0L	Red/Black

TEST PINS NO. 40 & 60 (PWR GND) WIRE COLOR ID

Application	Wire Color
Escort 1.9L & Tracer 1.9L	Black/Green
Continental, Crown Victoria, Grand Marquis & Mustang 2.3L	Black
Mustang 5.0L, Probe 3.0L, Town Car	Black/White
All Other Models	Black/Light Green

MAF SIGNAL VOLTAGE ⁽¹⁾

Application

Volts

Idle

20 MPH

1.1

40 MPH

1.7

60 MPH

2.1

⁽¹⁾	MAF signal voltage is typical for normal operating temperature. Voltage signal may vary due to engine load and temperature.

NOTE: Code 26/159 may be caused by use of a garage exhaust ventilation system. Ensure vehicle is vented to outside atmosphere before repeating QUICK TEST .

1) Code 26/159: Check VPWR Circuit Voltage Turn ignition off. Disconnect MAF sensor connector. Set DVOM on 20-volt scale. Turn ignition on. Measure voltage between VPWR terminal at MAF sensor wiring harness connector and negative battery terminal. If voltage is less than 10.5 volts, repair open in VPWR circuit and repeat QUICK TEST . If voltage is 10.5 volts or more, go to step 2).

2) Check MAF Sensor Ground Turn ignition on. Disconnect MAF sensor. Measure voltage between VPWR terminal and PWR GND terminal at MAF sensor connector. If voltage is less than 10.5 volts, repair open PWR GND circuit. Connect MAF sensor, and repeat QUICK TEST . If voltage is 10.5 volts or more, go to step 10).

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 2) to step 10). No test procedures have been omitted.

10) Code 66/157 Or 72/129: Check Continuity Of MAF & VPWR Circuits Continuous Memory Code 66/157 indicates MAF signal was less than 0.4 volt sometime during last 80 warm-up cycles. KOER Code 72/129 indicates insufficient MAF change during DYNAMIC RESPONSE TEST. Possible causes for this fault are:

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

Turn ignition off. Disconnect MAF sensor. Disconnect and inspect 60-pin connector at ECA. Service if necessary. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving ECA disconnected. Measure resistance between VPWR terminal at MAF sensor wiring harness connector and test pins No. 37 and 57 at breakout box. On Mustang 2.3L, measure resistance between MAF terminal at MAF sensor wiring harness connector and test pin No. 14 at breakout box. On all other models, measure resistance between MAF terminal at MAF sensor wiring harness connector and test pin No. 50 at breakout box. If all resistances are less than 5 ohms, go to step 11). If any resistance is 5 ohms or more, repair open MAF circuit and repeat QUICK TEST .

11) Check MAF & MAF RTN Circuit On Mustang 2.3L, measure resistance between test pin No. 14 and test pins No. 15, 40 and 60 at breakout box. On all other models, measure resistance between test pin No. 50 and test pins No. 9, 40 and 60 at breakout box. If resistance in any circuit is less than 10,000 ohms, repair short circuit and repeat QUICK TEST . If all circuit resistances are 10,000 ohms or more, go to step 12).

12) Check Continuity Of PWR GND Circuit Turn ignition off. Set DVOM on 200-ohm scale. Measure resistance between PWR GND terminal at MAF sensor wiring harness connector and negative battery terminal. If resistance is 10 ohms or more, repair open PWR GND circuit and repeat QUICK TEST . If resistance is less than 10 ohms, go to next step.

13) Check Continuity Of MAF RTN Circuit On Mustang 2.3L, measure resistance between MAF RTN terminal at MAF sensor wiring harness connector and test pin No. 15 at breakout box. On all other models, measure resistance between MAF RTN terminal at MAF sensor wiring harness connector and test pin No. 9 at breakout box. If resistance is less than 5 ohms, go to step 14). If resistance is 5 ohms or more, repair open MAF RTN circuit and repeat QUICK TEST .

14) Check MAF Signal For Short To Ground Turn ignition off. Disconnect MAF sensor. Connect ECA to breakout box. On Mustang 2.3L, measure resistance between test pin No. 14 and test pins No. 15, 40 and 60 at breakout box. On all other models, measure resistance between test pin No. 50 and pins No. 9, 40 and 60 at breakout box. If any circuit resistance is less than 10,000 ohms, replace ECA and repeat QUICK TEST . If each circuit resistance is 10,000 ohms or more, go to step 15).

15) Check MAF Circuit Output Turn ignition off. Connect MAF sensor wiring harness connector. Set DVOM on 20-volt scale. Start engine. On Mustang 2.3L, measure voltage between test pin No. 14 at breakout box and negative battery terminal. On all other models, measure voltage between test pin No. 50 at breakout box and negative battery terminal. If voltage is 0.4-1.5 volts, go to step 16). If voltage is not 0.4-1.5 volts, replace MAF sensor. Repeat QUICK TEST .

16) Check MAF Circuit Output Start engine. On Mustang 2.3L, measure voltage between test pin No. 14 and test pin No. 15 at breakout box. On all other models, measure voltage between test pins No. 9 and 50 at breakout box. If voltage is 0.4-1.5 volts, replace ECA. If voltage is not 0.4-1.5 volts, replace MAF sensor. Repeat QUICK TEST .

NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 16) to step 20). No test procedures have been omitted.

20) Code 56/158 Turn ignition off. Disconnect MAF sensor wiring harness connector. Start engine, and allow it to idle for one minute. Turn ignition off. Repeat KOEO (KEY ON ENGINE OFF) SELF-TEST. See procedures in KOEO SELF-TEST under QUICK TEST. If Code 66 or 157 is present, replace MAF sensor and repeat QUICK TEST . If Code 66 or 157 is not present, go to step 21).

21) Check MAF Circuit For Short To VPWR Turn ignition off. Disconnect ECA 60-pin connector, and inspect it for damaged or corroded terminals. Service if necessary. Measure resistance between MAF and VPWR terminals at MAF sensor wiring harness connector. If resistance is 10,000 ohms or more, replace ECA and repeat QUICK TEST . If resistance is less than 10,000 ohms, repair short circuit. Remove breakout box, and repeat QUICK TEST.