Fuel Injectors, Checking

Fuel Injectors, Checking

The following test procedure is used to diagnose all fuel injectors.

Special tools, testers and auxiliary items required

• multimeter.

• Diode test lamp (12V).

• Wiring diagram.

Test requirements

• The Fuel Injector Fuse 27 in Fuse Box C is OK.





• The Engine Speed (RPM) Sensor (G28) OK, checking => [ Engine Speed Sensor, Checking ] Engine Speed Sensor, Checking.

• Battery voltage at least 12.5 volts.

• All electrical consumers such as, lights and rear window defroster, switched off.

• Vehicles with automatic transmission, shift selector lever into position "P" or "N".

• A/C switched off.

• Ground (GND) connections between engine/transmission/chassis OK.

• Ignition switched off.

- Observe safety precautions.

- Observe rules for cleanliness.

Test procedure

- Perform a preliminary check to verify the customers complaint. Refer to => [ Preliminary Check ] Preliminary Check

Start diagnosis

- Remove the engine cover with air filter.

- Disconnect the Fuel Injector electrical harness connectors from Fuel Injectors (N30, N31, N32, N33, N83).

Checking internal resistance

- Using a multimeter, check the Fuel Injector electrical terminals 1 to 2 for resistance.





Specified value: 10.0 to 18.5 ohms (at approx. 20° C)

If the specified value was not obtained:

- Replace the malfunctioning Fuel Injector.

If the specified value was obtained:

Checking activation and wiring

- Connect a Diode test lamp (12V) to the electrical harness connector terminals 1 and 2 of the Fuel Injector to be tested.





- Operate the starter and test the activation of the Fuel Injector.

LED should flicker.

- Switch the ignition off.

If LED does not flicker:

- Remove the Fuel Pump Relay (J17).

- Connect a jumper between the Fuel pump relay terminals 30 and 87

- Turn the ignition switch ON.

- Using a test lamp connected to ground, check terminal 1 of the Fuel Injector to be tested. The lamp should be ON.

- If the test lamp did not turn on, locate the open or high resistance in the voltage supply circuit.

- If the voltage supply was OK:

If the manufacturers test box is being used, perform the following step.

- Install the test box.

If the manufacturers test box is not being used, perform the following step.

- Remove the Motronic Engine Control Module (ECM) (J623). Refer to => [ Motronic Engine Control Module, Replacing ] Motronic Engine Control Module, Replacing.

- Using a multimeter, check the Fuel Injector electrical harness connector terminals to the Motronic Engine Control Module (ECM) (J623) electrical harness connector T121 terminals for an open circuit.





Specified value: 1.5 ohms Max.

If the specification is not obtained:

- Check the wiring for an open, high resistance or short to voltage or ground.

- Check the electrical harness connector for damage, corrosion, loose or broken terminals.

- If necessary, repair the faulty wiring.

If no malfunction is detected in the wiring:

- Replace the Motronic Engine Control Module (ECM) (J623). Refer to => [ Motronic Engine Control Module, Replacing ] Motronic Engine Control Module, Replacing.

- Install the engine cover with air filter.

Final procedures

After the repair work, the following work steps must be performed in the following sequence:

1. Check the DTC memory. Refer to => [ Diagnostic Mode 03 - Read DTC Memory ] Diagnostic Mode 03 - Read DTC Memory.

2. If necessary, erase the DTC memory. Refer to => [ Diagnostic Mode 04 - Erase DTC Memory ] Diagnostic Mode 04 - Erase DTC Memory.

3. If the DTC memory was erased, generate readiness code. Refer to => [ Readiness Code ] Readiness Code.