Checking the injector valves / idle switch (VW Passat B3)

Mono-Jetronic, Mono-Motronic

If the engine does not start, you should always first check whether the injector is injecting fuel at all and whether there is an ignition spark.

The forced idle switch can only be tested with the engine running. The switch is designed to stop the fuel supply when the engine is running in forced idle mode (the car moves without pressing the gas pedal), as soon as the crankshaft speed exceeds 1500 1/min.

Check fuse #18, replace if necessary.

By polling the memory device for fault codes, ensure that there is a speed signal from the Hall sensor to the control unit.

Check the performance of the fuel pump, see below.

Checking the valve injector

Remove the air intake guide housing from the central injection system.



Ask an assistant to turn on the starter and check whether the valve injector is injecting fuel. A trace of the fuel stream should be visible on the throttle valve.

If the injector does not inject fuel, check the resistance, the presence of supply voltage and the preliminary resistance of the injector.





Press the locking metal bracket and disconnect plug "1" from connector "2".

Measure the resistance of the valve injector between the middle contacts of connector "2". The prescribed value is 1.2-1.6 Ohm. If the measured value does not match the prescribed value, replace the valve injector.

Note: The specified value is only for an ambient temperature in the range of +15°C to +30°C. If necessary, place the vehicle in a suitable place (garage) and wait for some time until the temperature of the valve injector reaches the specified value.

Check for supply voltage. To do this, connect a lamp on semiconductor diodes to both middle contacts of plug "1" and turn on the starter. The LED should blink. If the LED does not blink, check the preliminary resistance.




To do this, disconnect the plug of the pre-resistance circuit and check the resistance. The prescribed resistance value is 3-4 ohms. If necessary, replace the pre-resistance.

If no fault is found, perform an electrical check of the Mono-Jetronic system, see below.

Checking the idle speed switch

Warm up the engine until the coolant temperature is at least +60°C, then turn it off.

Remove the air intake guide shroud.

Start the engine and let it idle. Visually check for a stream of fuel in the direction of the throttle valve.

Using the throttle lever, add gas and increase the engine crankshaft speed to 3000 rpm, then quickly release the gas and observe the fuel flow.

The flow of fuel should be interrupted briefly until the engine speed decreases again. This is a sign that the fuel cut-off switch is functioning.

Turn off the ignition and check the valve injector for leaks. No more than two drops of fuel should come out within a minute.

Screw on the air intake guide cover.