EZ-117K and EZ-118K Control Units
 

EZ-117K and EZ-118K Control Units

Test Light
This article describes how to read fault codes from 740s that are equipped with the EZ-117K or EZ-118K ECU. A list of applicable engines is shown below.

ECU Type........Engine..........Model Years..........ECU Volvo Part Number
EZ-117K.........B230F...........1985-1988............1336505-1
EZ-117K.........B230FT.........1985-1989............1346469-8
EZ-118K.........B200E...........1985-1991............1336800-6*
EZ-118K.........B230E...........1985-1991............1336503-6*
EZ-118K.........B230K...........1985-1986............1336506-9
EZ-118K.........B230KH.........1987-1990............1357196-3

*Also applies to 1991 940 with B200E/B230E.

These ECUs have a very basic capability of reporting faults but it is nonetheless a useful feature for diagnosing some ignition faults. A list of fault codes is provided below.


Light flashes: 1 ☼
Test conditions: Wide open throttle
Symptom: The ECU has sensed engine knock and retarded the ignition by the maximum amount.
Possible causes: 1. The ignition timing is too advanced. 2. Faulty or incorrectly torqued spark plug. 3. The octane rating of the petrol is too low. 4. The fuel pressure is too low or an injector is restricted.
Possible solutions / actions: 1. Check/adjust ignition timing. 2. Torque or replace spark plugs. 3. Fill up car with petrol of correct octane rating (see specifications in owner’s manual for correct octane rating). 4. Test fuel pressure. Clean the fuel injectors.


Light flashes: 2 ☼ ☼ (B230K and B230KH only)
Possible causes: 1. Faulty temperature sensor.
Possible solutions / actions: 1. Measure resistance of temperature sensor. It should read 1.9kΩ at 22ºC. 2. Check integrity of wiring to temperature sensor. 3. Replace temperature sensor.


Light flashes: 4 ☼ ☼ ☼ ☼
Test conditions: Engine is idling or engine speed is greater than 3150rpm.
Symptom: The ignition is retarded by the maximum amount at high engine load. Loss of engine power and driveability.
Possible causes: 1. Knock sensor disconnected. 2. Knock sensor improperly tightened.
Possible solutions / actions: 1. Check integrity of knock sensor and the wiring thereto. 2. Tighten knock sensor to correct torque. Knock sensors fitted until 1986 were particularly sensitive to tightening torque. 3. If wiring is OK and the knock sensor is correctly tightened then suspect a faulty knock sensor or a faulty ECU.


Light flashes: 5 ☼ ☼ ☼ ☼ ☼
Test conditions: Open throttle switch (accelerator pedal slightly depressed). Engine running at light load.
Symptom: Faulty load signal from fuel system control unit, causing reduced timing advance. Loss of engine power and driveability.
Possible causes: 1. Open circuit in wire between terminal 24 on fuel system control unit and terminal 8 on ignition system control unit. 2. Faulty ignition control unit or faulty fuel control unit.


Light flashes: 5 ☼ ☼ ☼ ☼ ☼ (EZ-118K only)
Test conditions: Engine idling.
Symptom: Insufficient advance of ignition timing. Loss of engine power and driveability.
Possible causes: 1. Damaged or disconnected vacuum hose between inlet manifold and ECU. 2. Damaged or disconnected vacuum hose inside ECU. This is quite likely. 3. Plugged nipple on inlet manifold. 4. Faulty pressure sensor inside ECU.
Possible solutions / actions: 1. Check integrity of vacuum hose between inlet manifold and ECU. 2. Apply vacuum to nipple on ECU and check that the vacuum is maintained for at least 10 seconds. Visually inspect the hose inside the ECU. 3. Clean nipple on inlet manifold. 4. If a faulty pressure sensor is suspected then replace the ECU.


Light flashes: 6 ☼ ☼ ☼ ☼ ☼ (B230K only)
If the test light flashes six times on a B230K then check the same items as for five flashes.


The car manufacturer’s suggested method of reading the fault codes is to connect up special tool 5280 (Volvo part number 9995280). However, this tool is simply an LED, resistor, and wiring. You can make your own code reader very cheaply. A standard red 5mm LED will do. I suggest a value of 680R to 1kΩ for the resistor. Solder the LED in series with the resistor; it doesn't matter whether you connect the resistor to the anode or cathode of the LED. Solder wires to the leads. Blu-tac the LED to the dashboard where it can be seen while driving and route the wires from the cabin into the engine bay (away from the fan and exhaust manifold). Connect it up as shown in the next diagram.
http://www.thejogger.webspace.virgin...lliam/led1.jpg

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Above: Location of the diagnostics socket.
　
Often, the diagnostics socket will have two wires connected to it. The one you need to connect to is the yellow/red wire. Preferably, use a spade crimp to connect to this socket. In case you're curious to know, the pink wire on the diagnostics socket operates the starter motor when connected to the battery positive terminal (so be careful with that). The pink wire is absent on some cars.
With the test light connected up, turn the ignition key to position II. The LED should alight. Start the car. The LED should extinguish when the engine speed exceeds 920rpm. Go for a drive and induce the test conditions given above.
If you would like to keep the test light on the dashboard permanently then I suggest you drill a hole in one of the spare switch blanks and mount it neatly inside an LED bezel. Alternatively you could use a spare warning lamp in the instrument cluster, but be warned that those are 1.2W filament lamps and not LEDs. Therefore, to use one of the filament lamps you should use a transistor to switch on the lamp.


ECU Vacuum Hose
There is a yellow plastic vacuum line connected to the inlet manifold that runs along the bulkhead before entering the cabin where it attaches to the control unit next to the throttle pedal. This vacuum line allows the control unit to sense the level of vacuum in the manifold, which is necessary for computing engine timing. If you conducted the LED test as detailed above and you saw five or six flashes of the LED then you might want to check this vacuum line. To test the control unit, connect a short piece of 3.3mm rubber hose directly to the control unit and suck it. It should not be possible to draw air through the hose unless there is a leak. If there is a leak you would hear a faint noise from inside the control unit as you suck the hose. I tested two control units – one from a B230K and one from a B230KH – and both had vacuum issues. On the B230K control unit a small hose inside had become disconnected. On the B230KH control unit the small hose inside was badly split. According to the 700 ignition systems manual[1], when the load signal is not present the control unit uses the speed signal to adjust timing and 'operates in accordance with the pre-programmed , full-load timing setting' when the throttle idle switch is open.

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Above: ECU from a 1986 740 GL. The hose was disconnected.

http://www.thejogger.webspace.virgin...l_565b227b.jpg
Above: ECU from a 1988 740. The hose was split.

References
[1] Service Manual, Ignition sytems, 700 1982-, TP31397/1, Volvo, July 1989.