F.A.Q. - Diagnostic unit - how to use and code definitions
Ben Harris has provided us with information on the diagnostic function of later Volvo 480 models. All Volvos built from January 1991 and onwards should have a diagnostic unit on the front-left strut tower, in the engine bay:
CEM III has an integrated diagnostic system for fault tracing operations. The diagnostic system has 5 different test functions, namely:
- Function 1, Readout of faults stored in the memory.
- Function 2, Testing input signals.
- Function 3, Testing output signals.
- Function 4, Testing individual output signals.
- Function 5, Information concerning the data and status of the CEM.
Communication with the diagnostic system takes place with the aid of a diagnostic tester. This is located in the engine compartment on the turret of the left-hand MacPherson strut.
On the diagnostic tester there is a button, a lamp (LED) and a selector cable. When tracing faults on vehicles equipped with CEM III, the selector cable is inserted in position 5. The required test function is selected by pressing the button once, twice or three times, etc., for 0.5 seconds.
The data stored in the memory are indicated by a fault code which is formed by the flashing of the LED on the diagnostic tester. The code always consists of three consecutive series of flashes which together form a number consisting of three digits.
Each series of 1, 2, or 3 flashes, etc., arrives at 3-second intervals. This makes it easy to distinguish between each series (digit).
Note! The LED of the car alarm system also flashes.
In the event of failure of the battery voltage, the diagnostic data will be lost.
Test function 1 - Readout of faults stored in the memory.
The diagnostic system of the CEM continuously monitors its own functions. If a malfunction occurs in the system, this will be stored in the memory of the diagnostic system as a fault 27 different malfunctions can be identified and stored in the memory as fault codes. There is also a code (111 ) which indicates when there are no faults in the system. Test function 1 is activated by pressing the button once.After the faults have been remedied and having done two readouts of the fault codes, the memory function can be erased. This is done as follows:
- Keep the button pressed in for at least 5 seconds and then release it.
- The diode lights up after 1.5 seconds.
- Depress the button one more time within 5 seconds and keep it pressed in for at least 5 seconds.
- A new readout of test function 1 should indicate flash code 111.
| 1-1-1 | No faults stored |
| 2-1-2 | Car alarm disarmed |
| 2-1-3 * | Central locking system |
| 2-1-5 | Rear window heating, input |
| 2-1-6 | Driver's window open, input |
| 2-2-7 | Car alarm armed |
| 2-5-1 | Driver's window closed |
| 4-1-1 | Seat belt warning |
| 4-1-2 * | Status output (alarm) |
| 4-1-4 | Door open, output |
| 4-1-5 | Interior light |
| 4-3-2 | Central locking system, closed |
| 4-3-3 | Central locking system, open |
| 4-3-4 | Windows + sun roof, operation |
| 4-3-5 | Driver's window open, output |
| 4-4-1 | Windows and sun roof, closed |
| 4-4-3 | Rear window heating |
| 4-4-4 | Windscreen wiper, output |
| 4-4-5 | Headlight washer |
| 4-5-1 | Rear window wiper |
| 4-5-2 | Start interlock |
| 4-5-3 * | LED, central locking |
| 4-5-4 | Direction indicator switch |
| 4-5-5 | Auxiliary driving lights, output |
| * market-dependent | |
Test Function 2 - Testing input signals.
With test function 2 all the Input signals of the CEM can be tested. By 'trying' a switch oneself a flash code is given by the LED of the car alarm system and the LED on the diagnostic tester, indicating that a signal is entering the CEM.If no flash code is given, this indicates a faulty connection.
Test function 2 is activated by pressing the button twice. The LED will now flash and various functions can be 'tried'. Test function 2 is ended by selecting another test function.
After test function 2 has been selected, in the above example we lock the driver's door with the key. A microswitch incorporated in the lock then transmits a signal to the CEM instructing it, for example, to arm the car alarm system. When the CEM receives the signal from the microswitch, it transmits a flash code to the diagnostic tester, in this case 227.
When the door is unlocked with the key, the CEM receives a different signal from the microswitch. The CEM will now give code 212. In this way about 30 switches, or input signals, of the CEM can be tested.
| 1-1-1 | No faults stored |
| 2-1-1 | 75 (accessories) |
| 2-1-2 | Car alarm disarmed |
| 2-1-3 * | Central locking |
| 2-1-4 | 56a (lighting) |
| 2-1-5 | Rear window heating |
| 2-1-6 | Driver's window open, input |
| 2-1-7 | Hazard warning lights |
| 2-2-1 * | Accessory protection |
| 2-2-2 | Driver's door |
| 2-2-3 | Passenger's door |
| 2-2-4 | Bonnet - tailgate |
| 2-2-5 * | Code EUR/USA |
| 2-2-6 | 15 (ignition on) |
| 2-2-7 | Car alarm armed |
| 2-3-1 | 50 (starting) |
| 2-3-2 | Alternator D+(61) |
| 2-3-3 | 58 (lighting) |
| 2-3-4 | 56 (lighting) |
| 2-3-5 | Auxiliary driving lights, input |
| 2-3-6 | Rear window wiper, 18 sec |
| 2-3-7 | Rear window wiper, 6 sec |
| 2-4-1 | Reverse gear |
| 2-4-3 | Windscreen wiper, speed 1 |
| 2-4-4 | Intermittent wipe |
| 2-4-5 | Windscreen washer |
| 2-4-6 | Rear window washer |
| 2-4-7 | Seat belt contact |
| 2-5-1 | Driver's window, closed |
| 2-5-2 * | Key in |
| 2-5-3 * | IR input |
| 2-5-4 | Direction indicator switch |
| 2-5-5 | Full throttle switch, B18EP/FP |
| * market-dependent | |
Test function 3 - Testing output signals.
In test function 3 the output signals of the CEM are automatically activated according to a fixed cycle. Information concerning proper or faulty functioning is obtained by observation. If a function is faulty, this can be seen upon completion of the cycle by a readout of test function 1.Test function 3 is activated by pressing the button three times in succession (direction indicator stalk in left-turn or right-turn position). The program has been completed when the direction indicators start to flash.
After test function 3 has been selected, the CEM will automatically send command signals to components or functions in a fixed sequence. During the test program you will be able to see, for example, that:
- the interior light comes on;
- the central locking system at the passenger's side is activated (closed/opened);
- the driver's door window (and, if applicable, the tilting sun roof is opened and closed; the passenger's door window will only be closed if it is already open;
- the horn is activated as well as the rear window heating and the windscreen wipers (for 1 sweep), etc.
The entire test cycle (about 19 functions) is run through and completed once only.
Faulty or no output signals of the CEM:
- 1 can be observed visually during the test cycle (e.g. the windscreen wipers fail to operate) and
- 2 can be retrieved from the memory - after the test cycle has been completed - in the form of a fault code readout in test function 1.
Note! To observe all functions as well as possible, the direction indicator stalk should be moved to the left-turn or right-turn position, the driver's seat belt should be fastened and both door windows should be in the halfway open position.
| 4-1-1 | Seat belt warning |
| 4-1-2 * | Status output (car alarm) |
| 4-1-3 | LED output |
| 4-1-4 | Door open |
| 4-1-5 | Interior light |
| 4-3-2 | Central locking system, closed |
| 4-3-3 | Central locking system, open |
| 4-3-4 | Windows + sun roof, operation |
| 4-3-5 | Driver's window open output |
| 4-4-1 | Windows + sun roof, closed |
| 4-4-2 | Horn |
| 4-4-3 | Rear window wiper |
| 4-4-4 | Windscreen wiper |
| 4-4-5 | Headlight washer |
| 4-5-1 | Rear window heating |
| 4-5-3 * | LED, central locking system |
| 4-5-4 | Direction indicators |
| 4-5-5 | Auxiliary driving lights |
| * market-dependent | |
Test function 4 - Testing individual output signals.
In test function 4 the output signals are individually activated and tested.This is done as follows: select test function 4. The LED lights up. Then start to enter a code within 5 seconds, for example 442.
When the first digit of the code (4) has been entered, the LED lights up. Then enter the second digit (4) within 5 seconds, and so on. When the full code has been entered (442) the horn is activated 3 times for +/- 1 second. If more than one function is to be activated, test function 4 will have to be selected again.
| 4-1-1 | Seat belt warning |
| 4-1-2 * | Status output (car alarm) |
| 4-1-3 | LED output |
| 4-1-4 | Door open |
| 4-1-5 | Interior light |
| 4-3-2 | Central locking system, closed |
| 4-3-3 | Central locking system, open |
| 4-3-4 | Windows + sun roof, operation |
| 4-3-5 | Driver's window open output |
| 4-4-1 | Windows + sun roof, closed |
| 4-4-2 | Horn |
| 4-4-3 | Rear window wiper |
| 4-4-4 | Windscreen wiper |
| 4-4-5 | Headlight washer |
| 4-5-1 | Rear window heating |
| 4-5-3 * | LED, central locking system |
| 4-5-4 | Direction indicators |
| 4-5-5 | Auxiliary driving lights |
| * market-dependent | |
Test function 5 - Information concerning the data and status of the CEM.
With test function 5 a readout of the CEM specification can be obtained and the non-variable input signals can be tested, for example the (accessory) protection of a radio/cassette recorder.After test function 5 has been engaged a code has to be entered, for example 321; the system will then respond with flash code 211, indicating that this version is CEM III.