Function of Components



D-Jetronic components have largely become rare and sometimes very expensive. Therefore many parts are offered and installed, which do NOT fit to the D-Jetronic installed at Volvo.

Therefore always make sure you have the correct Bosch number and consult it for identification.

See and compare the numbers in the Bosch Equipment List.

The following parts should be placed in personal storage as a precautionary measure and procured at parts markets in case of possible slaughter:

  • Control unit (ECU)
  • Pressure Sensor
  • Throttle Position Switch (TPS): newer version (cover clipped) First version (cover with 4 screws) should not be installed any more due to heavy wear.
  • Impulse generator for ignition distributor (bit)
  • Intake manifold without hairline cracks and with good throttle valve shaft bearing
  • Temperature Sensor Coolant (NTC2) with brass housing (non-magnetic) instead of the steel housing (black socket)
  • System Pressure Regulator adjustable to min. 2.1 bar (prefered 2.2 bar)
  • Thermal Time Switch (TTS) 0 280 130 200
  • Auxiliary Air Regulator (AAR) 280 140 013, also the electrical one from the K-Jetronic can be used; 0 280 140 100, (+12V from pump relay connection 87 switch on, ground from intake manifold)

Still available or usable (status 2019)

  • Injection Wiring Harness at Buttkereit
  • Replacement of the original Ignition Distributor by 123ignition (with group triggering)
  • Fuel Pump from K-Jetronic or Pierburg
  • Injector Valves 0 280 150 036 (blue) and 0 120 150043 (yellow) partly still in stock at dealers or garages
  • Cold Start Valve 0 280 170 010
  • Temperature Sensor I (intake air) 0 280 130 006
  • Temperature Sensor II (coolant water) 0 280 130 014

    The Bosch D-Jetronic was introduced by Volvo as the first electronic injection system on the 1800E for the first model year 1970. Since this system is known today only to a few specialists, a functional description of the individual components is given below.

Electronic Unit (ECU)

The control unit processes the input values of the various sensors and controls the injection valves.

1. Version Bosch 0280 000 009 09.1969 – 05.1970 without CO pot-meter
2. Version Bosch 0280 000 017 06-1970 – 05.1971 without CO-pot-meter
3. Version Bosch 0280 000 034 06.1971 – 07.1973 with CO-pot-meter

In versions 1. and 2. the Cold Start Valve is still controlled by the Control Unit (ECU) via an extra relay. Max. 7 seconds.

With the 3rd version, the Cold Start Valve is activated by the Thermal Timer Switch, triggered by the magnetic switch of the starter (connection 50). The injection time is therefore dependent on the running time of the starter and the temperature of the Thermal Timer Switch (TTS).

When using the ECU with version 3 it is absolutely necessary to add a TTS for a correct cold start.

The auxiliary relay is not required. Only two relays remain in the engine compartment. (Main and Pump Relay)

Important Note:
The main relay may ONLY be replaced by the original with blocking diode and marked with a blue dot, Bosch 0 332 003 025 Here “NEVER” use a normal working current relay. Risk of damage to the control unit (ECU).Arbeitstrom-Relais nehmen. Gefahr für die Beschädigung des Steuergerätes (ECU).

Signal inputs:
The intake manifold pressure is sensed by the Pressure Sensor. The different outside air pressure is also recorded by the barometer box. This also results in height compensation.

Water temperature is measured by the water Temperature Sensor II.

Intake air temperature via the intake air Temperature Sensor I.

In addition, the speed signal via the trigger contacts (bit) in the lower distributor.

The throttle Position Switch (TPS) supplies the idle signal (CO setting on the potentiometer) and the signal for thrust cut-off) and,

as well as signals for TPS and movement (acceleration and deceleration).

The injection valves are only activated, when the signal from the trigger contacts (bit) in the lower distributor comes when the engine is started. At the same time the fuel pump is activated.


The roller cell pump of the wet type, delivers permanently fuel under the following conditions:


  • When the ignition is switched on, it is briefly activated by the control unit (approx. 1 second) to build up the admission pressure.
  • The pump only continues to run if the signals from the trigger contacts (bit) under the distributer comes regularly.
  • The pump may ONLY deliver when the engine is running. Risk of accidents and fire as well as danger of flooding in the engine compartment and
      in case of leakage in the system.
System Pressure Regulator

It controls the system pressure to a constant value. The regulator is equipped with a diaphragm (pressure membrane adjustable). Excess fuel is returned to the tank via the return line.

Recommended setting pressure 2.1 ± 0.1 bar (prefered 2.2bar)

Pressure sensor

The negative pressure in the intake manifold (that means, pressure is lower than the pressure of the outside air) varies greatly (at any engine speed) with variations in throttle opening and with the load. The pressure sensor compares the relative air pressure inside and outside the intake manifold and supplies an analog voltage to the ECU. The lower the negative pressure, the more the mixture is enriched.

Temperature Sensor I Intake air

In the VOLVO 1800E/ES, the Temperature Sensor I for intake air (NTC1) is installed in the engine compartment at the rear edge of the air filter housing (installation thread M8) and measures the temperature of the incoming air. However, it has little influence on the mixture.

Increase after removal + 0.5% CO more.

Temperature Sensor II Coolant Water

The Temperature Sensor II for coolant water (NTC2) is screwed into the cylinder head between the manifold suction pipe and the additional air slide (screw-in thread M10x1), and measures the temperature in the coolant circuit.

In the Volvo 1800E, a temperature sensor was first installed in a steel housing from September 1969 (Bosch 280 130 009). After a few months there was a recall action, because the sensor was faulty and there was a malfunction in the engine running. A new sensor in a brass housing was introduced in January 1970 (Bosch 280 130 014). The insulator with the plug connection is now dark brown instead of black. These colors are difficult to distinguish. The safe method: Use a magnet to check whether a sensor with a steel or brass housing is installed. The correct sensor can also be identified by the embossed Bosch number 014.

Ignition Distributor Trigging Contacts ("bit")

The trip contacts (RPM detection) are mounted on a U-shaped plate. The construction reminds optically of a set of teeth (“bit”). They are located at the bottom of the ignition distributor with separate access and are actuated by two cams.

They trigger the injection valves in two groups: 

  • Four cylinders: One group = 2 injection valves
  • Six cylinders: One group = 3 injection valves
Cold Start Valve

It injects additional fuel during cold starts (up to max. 35°C) as long as the starter is running.
Max. Injection time 7 seconds.

Up to model year 05.1971 the control unit is controlled by a relay. From model year 06.71 on: Control via a thermo timer switch without relay.

The switching is done by the thermo timer (retrofit when replacing the control unit from 06.71 on) see also information in the paragraph above.

At the rear of the magnetic switch there is a 4mm plug-in flag. This plug-in tag has plus if the magnetic switch is activated. From there Plus (+) goes over the thermal timer switch and to the cold start valve. When the engine is cold, the thermo timer connects the ground to the cold start valve, which then injects fuel when it gets plus from the starter at the same time. As long as plus is coming from the starter motor to the thermo timer, a bimetal spring is heated inside, which switches off the mass to the cold start valve after max. 7 seconds.

If the temperature of the engine is above 35°C the thermo timer does not switch on the cold start valve anymore. A perfect cold start is only possible with a correctly functioning thermal timer switch.

Identification of the two connections on the TZS: The ground connection has a cold connection to ground (ground housing resistance=0 Ω). Warm the ground connection is interrupted. At the positive input a cold resistance (bimetal) to ground can be measured.

Fuel Injectors

The Injection Valves are clocked in the milisecond range. An increase in the clock rate results in a richer mixture.

The voltage between the two connections on the valve is in the range of 0.3 to 4.0 volts.

Attention! Never drive valves directly with 12 volts, otherwise they will go out.

Throttle Position Switch (TPS)

The throttle Valve Switch (TPS) is screwed to the intake socket of the collecting suction pipe and is controlled directly by the throttle valve shaft. The shaft actuates a rotor in the switch (sliding contact slides over the contact comb). The TPS is connected to the cable harness of the D-Jetronic with a 4-pole connector.

The switch has three functions: 

  • Sliding operation: Signal to the control unit so that no fuel is injected. For example when braking with the engine.
  • Acceleration: Signals to the control unit so that a precisely determined amount of fuel is injected in addition to the normal amount of fuel, i.e. a so-called transitional enrichment.
  • Idle speed detection
Thermal Timer Switch (TTS)

The Thermal Timer Switch (TTS) receives +12V from the contact on the magnetic switch when starting. This switches ground via a bimetal spring to the cold start valve. As soon as starting , the bimetal spring is heated by a heating resistor. Depending on the output temperature up to 7 seconds. If the bimetal is heated or the ambient temperature is higher than 35°C, the cold start valve does not need to be activated. The bimetal spring then switches off the ground. You can find further information under modifications.

With old control units (until 05.1971) the cold start valve is controlled by the temperature value of the water temperature sensor. The installation of the newer version (from 06.1971) is possible, but an additional thermo timer switch must be installed and wired.
You can find further information under modifications.

Cold Start Relais

With the old version there are three relays in the engine compartment, from 06.1971 on only their two.

  • Cold start relay (not applicable from 06.1971)
  • Main relay, with blue dot, for the power supply of the control unit. This relay has an integrated blocking diode and may only be replaced by an equivalent relay. Otherwise danger by destruction of the control unit.
  • Pump relay, controlled by the control unit. The relays for the cold start valve and the fuel pump are normal 4-pole working current relays

To test the injection pump, the connections 30 and 87 on the pump relay can be disconnected and then short-circuited with a bypass.

Auxiliary Air Regulator (AAR)

The Auxiliary Air Regulator is a valve operated by a wax thermostat, which opens an orifice when the engine is cold in order to increase idle speed via a bypass. It is located in the water circuit at the cylinder head and closes when heated.

It is now available again (but at an exorbitant price), but can be replaced by the electrically heated auxiliary air slide of the K-Jetronic from the B21 and B23E. The +connection of the electrically heated additional air slide of the K-Jetronic has to be connected to the output of the pump relay (contact 87). Connection ground at the intake manifold.

There should also be the wax thermostat separately again. Hermann Ebner:, takes over the installation in the ZLS. The defective ZLS can be sent in and Hermann Ebner will draw for a competent conversion in the exchange procedure.

Contrary to other unqualified assertions, the ZLS “only” influences the engine speed, it does not lose weight, nor does it have any influence on possible false air.

Fuel Filter

Replace the fuel filter. Change interval used to be 40,000 km.  If the flow rate is too low, the mixture will lean out around the top RPM.

Change more often if the tank is left standing in the cold season, because the fuel additives attack the tank.

Influences of the positioning value transmitters

As soon as starting the engine, the control unit receives pulses from the trigger contacts under the distributer. It switches on the fuel pump and trigger the injection valves, depending on the intake air, engine temperature and pressure sensor switch values.

  • Cold engine: Greater through higher clock rate, which is reduced as the engine warms up
  • When the engine is warm, the pressure sensor value is the main control value
  • Idle speed: High vacuum
  • Partial load range: Reduced vacuum
  • Full load: vacuum = 0

Sensitive acceleration is noticeable through lower consumption.

Since the pressure sensor values are stored in the control unit, every camshaft change (especially with very sharp shafts) is noticeable. Since the vacuum values change into the negative due to other control times, the injection program is no longer correct. Therefore please use only the standard D-shaft for B20 E/F. (164: C-shaft), otherwise there could be trouble.

Expired camshafts have a considerable influence on the pressure sensor values due to gas oscillations. As the pressure sensor is adjusted to the engine, there are different pressure sensors, e.g. for E and F.

D-Jetronic, Priciples of Operation

1 Control Unit (ECU) 6 Cold Start Valve 11 Trottle Position Switch
2 Injetor Valve 7 Fuel Pump 12 Ignition Distributer Trigger
3 Pressure Sensor 8 Fuel Filter 13 Temp. Sensor I Air Intake
4 Temp. Sensor ll Coolant Water 9 Pressure Regulator 14 Fuel Tank
5 Termal  Time Switch 10 Auxiliary Air Regulator 15 Main Relay for switching on the ECU

Important Note!

The main relay (15) may only be replaced by an original with “BLUE POINT”.
This contains blocking diodes to protect the control unit.

For the replacement components, where appropriate, always compare the original Bosch number first and then the VOLVO part number.