944 Instruments, Economy Control & Burglar Alarm
Factory instrument-system service data for the 944 — how the economy (consumption) display and the upshift indicator work and which signals they need, removing and installing the instrument cluster, bench-checking the coolant-temperature, fuel-tank and oil-pressure gauges against the VAG 1301 test-unit tables, the burglar-alarm control-unit signals, and the cluster illumination-bulb wattages. USA-market notes are given in brackets.
Instrument-system service data for the 944. The economy (fuel-consumption) display and the upshift indicator are both built into the tachometer and share its electronics; the fuel, coolant-temperature, oil-pressure and voltmeter gauges are separate movements in the cluster. This page covers how the economy and upshift functions work and the signals they need, how the cluster comes out, how to bench-check each gauge against the factory test-unit values, the burglar-alarm control-unit signals, and the cluster bulb wattages. Resistances are in ohms, test-unit settings are dimensionless dial numbers, and bulb ratings are in watts, so those values are written as-is; temperatures and the one torque figure switch between unit systems.
Economy control and upshift indicator
Both systems are integrated into the tachometer. The economy control displays the instantaneous fuel consumption — in litres per 100 km, or in miles-per-gallon / gallons- per-hour on USA cars — computed from road speed and injection time. The upshift indicator (fitted to USA cars with manual transmission) lights when the car can be shifted up into the next-higher gear economically. It works in gears 1 through 4 and stays on until the next-higher gear is selected or the operating condition changes the display (for example coasting or full throttle).
The indicator lamp is designed to be legible in daylight and dims when the main lights are switched on. The electronic control for both systems lives inside the tachometer and, like the indicator lamp, cannot be replaced separately — a failure that survives the signal checks means replacing the tachometer.
Signals required
The economy control needs two inputs:
- Road speed — the Hall-sensor signal from the speedometer.
- Injection signal — the injection-time (ti) signal from the DME control unit.
The upshift indicator needs four inputs:
- Engine speed — the ignition signal (coil terminal 1).
- Coolant temperature.
- Road speed — the Hall-sensor signal from the speedometer.
- Injection time (ti) — from the DME control unit.
Checking the economy control
The economy control and upshift indicator share the same signal tests. At the tachometer, the economy/upshift plug is the square connector (plug A); the round connector (plug B) is the USA altitude-correction box. Terminal numbering on the tachometer body is 1 · 2 · 3 · HG across the top and 4 · 5 · 6 · H+ across the bottom.
- On the two-pin plug next to the DME control unit, terminal 1 (black wire) should show battery voltage with the ignition on.
- Terminal 2 of that plug carries the injection signal with the engine running — a square-wave that grows wider as engine speed rises (view it on an oscilloscope).
- Remove the tachometer (leave the plugs connected) to reach the speedometer Hall-sensor signals. Terminals 5 and H+ should show battery voltage with the ignition on.
- Connect a voltmeter to terminal HG (Hall-sensor pulse). Lift and turn the left front wheel slowly by hand: the voltage should rise and fall four times per wheel revolution, swinging from below 1 volt to above 6 volts (square-wave pulses).
If the upshift indicator itself is faulty, run the same tests, then two more:
- The coolant-temperature gauge must read correctly — its signal comes from tachometer terminal 4 and is passed on to the instrument cluster.
- Terminal 6 of the tachometer should carry the ignition pulse (ignition coil terminal
- with the engine running.
If no fault is found after these checks, verify the wiring continuity and connector contact, and replace the tachometer only if necessary.
Removing and installing the instrument cluster
For the cluster used from the 1985/2 model:
- Pull off the steering-wheel cover plate by hand, unscrew the nut and take off the steering wheel.
- Unscrew and remove the instrument cover.
- Unscrew the instrument-cluster mounting screws.
- Unlock and take off the plug connections on the cluster, then withdraw it.
Reverse the sequence to install. When taking the speedometer out, handle it carefully. Inside the cluster the electronics sit on a printed circuit board / printed circuit; the solenoid is spot-welded and should be un-welded carefully on removal and cemented back if necessary.
Speedometer transmitter
The speedometer transmitter (sender) is on the left side of the transmission, next to the axle-shaft flange.
- Pull the plug off the transmitter.
- Loosen and unscrew the transmitter with a suitable tool. The lower hexagon belongs to the transmitter's mechanical drive — do not undo it.
Note: Observe the specified tightening torque when refitting the transmitter. Tightening torque 4 N·m3 ft·lb.
Checking the instruments
The coolant-temperature, fuel-tank and oil-pressure gauges are checked with the VAG 1301 test unit. Disconnect the connecting cable from the relevant sender, connect the test unit in its place, set the value from the table below, and switch on the ignition. If the gauge then reads correctly, the fault is the sender — replace it. If the gauge reads wrong or reads nothing, check the cable to the gauge and replace the gauge if necessary. One pointer-width to the left or right is a permissible deviation. The resistance column is the equivalent sender resistance at each point.
Coolant-temperature gauge — models 82–85
| Coolant temperature | Test-unit setting | Resistance (Ω) |
|---|---|---|
| 40 °C104 °F | 557–558 | 287.4 |
| 105 °C221 °F | 46–47 | 33.6 |
| 120 °C248 °F | 24–25 | 22.7 |
Coolant-temperature gauge — from the 85/2 model
| Coolant temperature | Test-unit setting | Resistance (Ω) |
|---|---|---|
| 40 °C104 °F | 557–558 | 287.4 |
| 60 °C140 °F | 247–248 | 134.0 |
| 80 °C176 °F | 117–118 | 69.1 |
| 100 °C212 °F | 55–56 | 38.5 |
| 115 °C239 °F | 30–31 | 25.8 |
Fuel gauge — models 82–85
See also Fuel Level Indication Problems and Repairs for diagnosing sender and gauge faults on the road.
| Tank level | Test-unit setting | Resistance (Ω) |
|---|---|---|
| Reserve | 122–123 | 71.6 |
| 1/4 | 96–97 | 58.7 |
| 1/2 | 47–48 | 34.5 |
| 3/4 | 9–10 | 15.3 |
| Full | no setting possible | 3.2 |
Fuel gauge — from the 85/2 model
| Tank level | Test-unit setting | Resistance (Ω) |
|---|---|---|
| Reserve | 105–106 | 63.2 |
| 1/4 | 63–64 | 42.2 |
| 1/2 | 21–22 | 21.2 |
| 3/4 | no setting possible | 8.6 |
| Full | no setting possible | 2.8 |
Oil-pressure gauge — models 82–85
| Oil pressure | Test-unit setting | Resistance (Ω) |
|---|---|---|
| 0 bar0 psi | no setting possible | 10.0 |
| 3 bar44 psi | 212–213 | 116.0 |
| 5 bar73 psi | 349–350 | 184.0 |
Oil-pressure gauge — from the 85/2 model
| Oil pressure | Test-unit setting | Resistance (Ω) |
|---|---|---|
| 1 bar15 psi | 37–38 | 29.6 |
| 2 bar29 psi | 110–111 | 65.3 |
| 3 bar44 psi | 177–178 | 98.9 |
| 4 bar58 psi | 246–247 | 133.6 |
| 5 bar73 psi | 349–350 | 184.0 |
The voltmeter shares the cluster with the oil-pressure gauge on one dual movement; there is no separate test-unit table for it — a reading roughly matching battery voltage with the engine running is the check.
Burglar alarm
Two arrangements are documented. On earlier cars the alarm's auxiliary control unit sits in the central electric system; from the 1989 model the alarm control unit sits in the passenger footwell behind the DME control unit. Check that the listed signals are present at the control-unit terminals.
Auxiliary control unit — earlier cars
Input signals (check at the base, with the relay removed):
- Terminal 1 — ground with a door or the tailgate open.
- Terminal 3 — ground.
- Terminal 4 — battery voltage (terminal 30).
- Terminal 8 — ground with the key in a door lock cylinder (driver's or passenger's) turned towards "closed", only while the cylinder is held there.
- Terminal 9 — ground when the lock cylinder is turned towards "open".
Output signals (check only with the relay fitted):
- Terminal 2 — ground if there is ground at terminal 8, or when the alarm arms about 25 seconds after the tailgate is closed (a short pulse of about 0.5 seconds only).
- Terminal 5 — battery voltage.
- Terminal 6 — ground if there is ground at terminal 9.
Alarm control unit — from the 1989 model
Input signals:
- Terminal 31 — ground.
- Terminal 30 — battery voltage.
- Terminal 15 — battery voltage with the ignition on.
- Terminal 61 — battery voltage with the engine running.
- Terminal T– — ground with a door or the tailgate open.
- Terminal MK — ground with the engine hood open or the radio removed.
- Terminal A — ground with the key in a door lock cylinder turned towards "open".
- Terminal E — ground when the lock cylinder is turned towards "closed".
Output signals:
- Terminal 87a — battery voltage with the ignition on.
- Terminal Hn — battery voltage, clocked, with the alarm primed and triggered (permanently clocked on Swiss cars).
Note: A relay in base G 18 of the central electric system operates the fog lamps and brake lamps as a visual warning in addition to the alarm horn on USA cars.
Instrument-cluster illumination bulbs
Bulb ratings for the cluster used from the 1985/2 model. These are fixed wattages — they do not convert:
| Location | Quantity | Rating |
|---|---|---|
| Warning/indicator lamps (bulb with holder) | 4 | 1.2 W |
| Instrument illumination (bulb with holder) | 16 | 1.2 W |
| Instrument illumination (bulb with holder) | 3 | 2 W |