Volvo Coupes/Sedans/Wagons 1970-1989 Repair Guide

LH-Jetronic, LH-II Jetronic and LH-Jetronic 2.2 Fuel Injection Systems


See Figure 1

The Bosch LH-Jetronic electronic fuel injection system became available on the B21F-LH engine in 1982 and on the B23F-LH in 1983. The complete system contains the following components: L-Jetronic Electronic Control Unit (ECU), airflow sensor, system relay, fuel pump relay, Lambda-Sond oxygen sensor, vacuum switch, electric fuel pump, coolant temperature sensor, fuel injectors, and the electronic control unit terminal for the Constant Idle Systems (CIS) if equipped. On the 1983 and later B23F-LH, the fuel injection and the CIS (constant idle speed) systems are both controlled by the same Electronic Control Unit mounted on the right side kick panel.

LH is an abbreviation of a German term which means "hot wire air mass meter." All the LH systems work on the principle of controlling injector duration, but instead of an air flow sensor flap to measure intake air quantity, these systems use a heated platinum wire to measure the air mass. In this manner, altitude influences are eliminated.

A very thin platinum wire is stretched across the air intake opening in the air-flow meter and forms part of a bridging circuit. The intake air flowing over the heated wire cools the wire, changing its electrical resistance according to the temperature. An electronic amplifier instantly responds to any such change and regulates the current to the wire so as to maintain it at a virtually constant temperature. The current necessary to maintain the wire temperature is the measure of the the air mass flowing into the induction system. This measurement is used by the ECU to determine the injector duration (opening time).

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Fig. Fig. 1: Exploded view of the LH-Jetronic air mass meter

Because dirt and impurities may accumulate on the wire and affect the voltage signal, the system is designed to clean the wire each time the engine is shut off. When the engine stops, the wire is heated to 1100-1900°F (593-1,038°C) for less than one second. This burns off any impurities which could cause false readings.


See Figures 2, 3, 4 and 5

The components within the fuel injection system are generally very reliable. Outright failure is not common, although reduced function may occur as a result of age and wear. Before jumping into the injection system and its very expensive pieces, check everything else which influences the system. The LH systems depend heavily on all other components being correct.

It is essential that compression, valve clearance, vacuum routing and flow, and throttle settings be checked and repaired if necessary. Spark plug wires, distributor cap, air filters and electrical connections (including blown fuses) can also cause you to look in the wrong place. A flaw in either the crankcase or evaporative emissions controls can cause hours of misdirected investigation. Simply stated, check the easy things first-repairing a loose ground connector can save you hundreds of dollars.

The fuel injection system is repaired simply be replacing the defective component. There are some adjustments that can be made to some components, but these require a high level of experience and special test equipment. To make resistance checks, use an ohmmeter and for continuity checks, a 12V test light. If the control unit is defective, return it to a qualified repair agency and install a new unit.

It is impossible to test the operation of the ECU without very expensive testing equipment. The easiest way to diagnose a failed ECU is to eliminate all other possibilities by testing the circuits it controls. If all the controlled circuits check good and a performance problem is still evident, the controller must be bad.


  1. With the ignition OFF , remove the right side kick panel and any necessary trim pieces, sill moldings, etc.
  3. Carefully release the catches on the ECU and pivot the connector down and away. The connector should come free of the box. If it doesn't, check for the cause of interference; don't force anything.
  5. With the connector free, remove the small retaining screws in the connector case. Gently slide the cover a few inches back along the cable. This exposes the body of the connector.
  7. The connector numbers are on the body of the connector. Notice the rows of square or rectangular holes along the side of the connector body. These are where you insert the probes of the volt-ohmeter. DO NOT insert the test probes into the front of the connector; this can damage the pins and induce other faults. When testing through the side holes, use only enough pressure to make good contact.
  9. When reassembling, work carefully and do not force the body of the plug into the cover. Make sure the wires are not crimped or under undue pressure.

System Grounds

The terminals should be numbered (embossed on the plastic housing) on the ECU in order to allow this test to be performed.

Connect the ohmmeter to a known ground and individually check terminals 11 and 25. On LH-2.2 systems, also check terminals 5 and 19. Resistance should be nearly zero in all cases. If ground checks show high resistance, check the ground connections at the intake manifold.

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Fig. Fig. 2: Be extremely careful when removing the ECU connector for testing

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Fig. Fig. 3: Location of LH-Jetronic 2.2 components-B280E/F engines

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Fig. Fig. 4: Location of LH-Jetronic 2.2 components-B230F engines

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Fig. Fig. 5: Location of LH-Jetronic II components-B23F engines

Coolant Temperature Sensor

See Figure 6

Connect the ohmmeter between ground and terminal 2. Resistance depends on coolant temperature (see chart). As a reference, if the coolant is at 68°F (20°C), look for readings of 2300-2700 ohms. If the coolant is at 176°F (80°C), expect readings of 300-360 ohms. Hint: if the ohm reading is incorrect, perform the test again at the pins of the sensor. If the readings are now correct, you have a wiring problem, not a sensor problem.

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Fig. Fig. 6: Coolant temperature sensor resistance varies with coolant temperature-B230F with LH-Jetronic 2.2 shown. Others with LH-Jetronic are similar within plus or minus 100 ohms

Throttle Switch (Throttle Valve Switch)

The terminals should be numbered on the unit in order to allow this test to be performed. If they are not, you will need to acquire a schematic or diagram of this component before testing can begin.

With the ohmmeter connected between ground and terminal 3, depress the accelerator pedal. The meter should show zero resistance in the idle position and infinite (open) in all other positions. Now connect the ohmmeter between ground and terminal 12. Again depress the accelerator pedal; look for zero resistance at full throttle and infinite at all other positions.

Double check any faulty readings at the switch on the intake manifold. If the the values are still wrong, adjust the switch or linkage or replace the switch.

Air Mass Meter: Current Supply and Ground

See Figure 7

Connect a jumper from terminal 21 to ground and leave in place. On Jetronic 2.2 systems, also jumper connector 17 to ground. Under the hood, gently peel back the rubber cover on the connector to the air mass meter.

On Jetronic II systems, connect the voltmeter between terminal 9 and ground, then between 9 and 36. In both cases the meter should show battery voltage.

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Fig. Fig. 7: Carefully remove the boot to test the circuits at the air mass meter

For Jetronic 2.2 systems, check between terminals 1 and 5 on the air mass meter, looking for battery voltage. Reinstall the protective rubber boot and remove the ground jumper(s) from the harness.

Now use the ohmmeter to check the resistance of the wire in the air mass sensor. For both types of systems, connect the probes to terminals 6 and 7 of the ECU harness (inside the car). Correct resistance is 3.7 ohms. Test the resistance between terminals 6 and 14. Expect a reading between 0 and 1000 ohms, depending on the CO setting established at the factory.

Air Mass Meter Burn-Off Current

The terminals should be numbered on the unit in order to allow this test to be performed. If they are not, you will need to acquire a schematic or diagram of this component before testing can begin.

This test is performed with the ECU harness connected.

Start the engine and allow it to warm up fully. Shut the engine off and peel back the rubber boot at the air mass meter connector. On Jetronic II systems, connect the voltmeter between terminals 8 and 36. Restart the motor and accelerate it to at least 2000 rpm. Switch the motor off and observe the voltmeter. After about 5 seconds, the meter should show about 1 volt for about 1 second. This shows that the burn-off cycle has started and finished. Remove the voltmeter and replace the connector boot.

For Jetronic 2.2 systems, connect the voltmeter between terminals 1 and 4. Accelerate the engine above 2100 rpm and then shut it off. After 4 seconds, the meter should deflect for one second. Remove the voltmeter and replace the connector boot.

Fuel Injectors

See Figures 8, 9, 10 and 11

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Fig. Fig. 8: Exploded view of the fuel injector rail-B230F engines

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Fig. Fig. 9: 1983 LH-Jetronic injector installation with clamp

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Fig. Fig. 10: LH-Jetronic fuel and electrical flow diagram

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Fig. Fig. 11: LH-Jetronic injection manifold-1982 and later B21 and B23F-LH models

A quick way to check injectors is simply to listen to them. With the engine running, touch a long shaft (such as a screwdriver) to the injector and listen to the opposite end. You should hear a distinct repeated clicking as the injector opens and closes. If one doesn't click, swap it with a known good one elsewhere in the system and reconnect the wires (don't get the wires interchanged). Listen again; if the bad one is still bad, replace it. If the known good one is now bad (and the first bad one now works), there is an electrical fault in the circuit to the injector.

Using an ohmmeter, you can check the injector resistance with the engine off. Disconnect the electrical lead to the injector and touch the leads to the two terminals. If the injector temperature is 68°F (20°C), resistance will be 16 ohms. Resistance will rise with injector temperature; its best to do this test on an engine which has not been run in several hours.