Air Flow Sensor Potentiometer

Motronic ECU Harness Connector (pin # Locations):

STATIC TEST

1. Make sure mechanical adjustments are correct (check sensor plate rest position, see FUEL SYSTEMS for adjustment).

2. Disconnect potentiometer from harness connector, and connect DVM to terminals #1 and #3 of harness connector, set to 20V DC scale.

3. Turn ignition "ON". Voltmeter should read 4.35 to 5.35 volts (reference voltage from pin #26 of ECU to terminal #1 of potentiometer). If reference voltage is not present, check for open or grounded circuit to ECU pin #26 or open circuit between potentiometer connector terminal #3 and ground, repair as necessary and continue test from next step. If circuits are OK, then there is no reference voltage from ECU (faulty ECU).

4. Set DVM to K-ohms and check resistance between pins #1 and #3 of potentiometer. Resistance should be approx. 4k ohms.

5. Check resistance between pins #1 and #2 of potentiometer with sensor plate in rest position. Resistance should be approx. 5K ohms and decrease gradually as sensor plate is raised.

DYNAMIC TEST

1. Make sure mechanical adjustments are correct (check sensor plate rest position, see FUEL SYSTEMS for adjustment).

Test Connections Using Self-made Parallel Test Leads:

2. Connect parallel test leads between respective terminals of potentiometer and its harness connector. Turn ignition "ON".

Air Flow Sensor Potentiometer Voltage Values:

3. Using DVM, check voltage between terminals #1 and #3 of potentiometer. Should be 4.35 to 5.35 volts. (Voltage "a", Fig. 1). If no voltage reading is obtained, see step 3 of static test.

4. Check voltage between terminals #2 and #3 of potentiometer (voltage "b", fig. 1). Voltage should fall within the range shown in Fig. 1, for the value of voltage "a" measured in previous step. If not, remove sealing compound from around trim screw and adjust potentiometer until correct value is obtained (best to be at the middle of the range). If correct value cannot be obtained, and sensor plate rest position is correct, then replace potentiometer.

5. Start engine and let idle. Repeat steps 3 and 4. Voltage "b" should fall in the range shown in Fig. 2. If voltage is below the prescribed range, check for vacuum leaks, check sensor plate movement for sticking. If no other problems are found, try adjusting the trim screw. If correct value cannot be obtained, replace potentiometer.