December 1999 Articles & Features

Launch Tech

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Ins & Outs of European Engine Management Systems

By Kerry Josson | December 1999

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European cars provide plenty in the way of self-diagnostics, once you know how to tap into their systems. Here are some tips to help you pull codes and data with the best of 'em.

The exact date may be open to debate, but it was about 1980 that the yuppie movement began. That's important to European carmakers because yuppies love to be trendy and chic and, having the money to afford it, as a group they became large purchasers of European vehicles. And that's important to you because now that these vehicles have been out of dealer care for quite some time, they're starting to require more frequent service.

It used to be that only specialty shops would handle driveability diagnoses on these cars, and experience and a few quick pin voltage checks would determine what went wrong. Of course, as systems became more complicated, some form of self-diagnostics was needed, and all the manufacturers seem to have gone in their own direction. In fact, in some cases, individual manufacturers have gone off in several different directions!

If you don't have the factory scan tools for all the European manufacturers, here are some methods for extracting DTCs with minimal equipment, as well as some of the other functions available to help you diagnose tough driveability problems on European nameplates.


In 1984, Audi started offering self-diagnostic capabilities on its 5000s, turbos, and Coupe GTs. Accessing the system is fairly simple: First, run the engine over 125 degrees F, and while it's running below 2000 rpm, close the wide-open throttle (WOT) switch with your hand, and keep the throttle's idle switch closed for 4 seconds. If the engine won't start, just crank it for at least 6 seconds. The tach will jump to 7000 rpm-not the rpm, just the tach.

Now, while holding all that, step on the brake pedal once to start the code sequence. By the way, you can let go of the throttle switches after 4 seconds. After you step on the brake pedal, the tach will move to a different rpm range and the Check Engine light (CEL) will be either on or off. Any combination of tach reading and CEL operation will yield a specific fault. Step on the brake pedal again to advance to the next code.

The only code I quite don't understand is a 6000-rpm reading with the CEL off. This supposedly means a bad idle switch. Well, if the switch were no good, how did we get into self-diagnostics in the first place! If there are no codes stored, the tach will stay at 7000. Also note that if the vehicle has a Hitachi control unit, the end-of-code sequence will be the tach stuck at 7000 with the CEL off; if it's a Bosch control unit, the first code will repeat.

Self-diagnostic procedures came to the fore in 1985 on Audi's 4000 models, and in '86 they started using these same self-diagnostic procedures on their 5000s. Be aware that Audi 4000 Quattro models never saw self-diagnostics. On models other than the Quattro, a four-digit trouble code can be accessed through the CEL by running the engine anywhere below 2000 rpm, or cranking the engine for at least 6 seconds while bridging two terminals. These terminals are located on the fuel pump relay, which is in the fuse/relay panel on the driver's-side cowl area, under the hood. By bridging these terminals together with a fuse for 4 seconds, the CEL would have one long flash followed by a series of four shorter flashes, which make up the code. This code will repeat, until the fuse is inserted again, for 4 seconds. This tells the computer to move on to the next code.

The ignition control unit codes will be displayed first. You repeat this procedure until the CEL flashes at 2-1/2-second intervals (no codes). Then you follow the same routine to extract fuel injection system codes, until the light again flashes at 2-1/2-second intervals.

You may notice that the engine's rpm may increase slightly; this is normal. If the CEL blinks twice, the knock sensor adjustment is at its maximum of 7.8 degree retard. If the light flashes three times, the throttle switch inputs aren't matching the MAP sensor readings. These things must be fixed before you can continue with self-diagnostics.

On most cars, self-diagnostic procedures are performed with the ignition key on and the engine off, but in the cases noted above, you must have the engine running. Because this system has no memory and cannot remember stored codes, always go on a spirited test drive before entering self-diagnostics. Also, trying to enter self-diagnostics with key on/engine off will get you into an output state check.

The procedure is the same as pulling codes: Insert a fuse into the relay for 4 seconds, and a code will be displayed, which represents the output being cycled. By repeating this procedure, you can cycle several outputs in a specific sequence. Note that on Audi's Coupe GT model, you must insert the fuel pump fuse to move from one output check to the next as well as close the WOT switch to activate the output. You may have a code output, but have nothing cycled on. Also, the control unit may output a code even if the system is not on the car.

In 1988, California required some form of self-diagnostics as well as a Check Engine light to indicate when there was a fault with emissions-related components. These emissions faults can be recorded in memory. On federal vehicles, these codes will be erased in the next key cycle.

Note that Audi 80 and 90 models with the 2.0-liter engine have a diagnostic output connector mounted near the airflow meter. By connecting an LED bulb wired through a 330-ohm, 1/4-watt resistor between battery positive and the diagnostic connector, you can watch DTCs blink out. A logic probe also works fine here.

To initiate the diagnostic procedure, you still have to use the fuse on the back of the fuel pump relay and follow the same procedures as before, but the engine need not be running. A code 4444 means there are no faults detected. After all the codes have been displayed and you get the 2-1/2-second flash, insert the fuse for 10 seconds to clear codes from memory.

Since you can get codes on this system with the key off, Audi had to alter how to get into its output state check. To do it, insert the fuse before turning on the ignition key, then close the full throttle switch. The ECU will spit out a code and cycle the output, but it will do it in a predetermined sequence.

In late '89, Audi altered its self-diagnostic procedures for federal models, as well as the model numbers of their cars. With the early-'89 models, you still had to use the fuse in the back of the fuel pump relay to access self-diagnostics. The codes will either blink out through the Check Engine light or through your LED test light connected to the diagnostic connector near the airflow meter. Those '89 models without a CEL have only volatile memory.

On late-'89 models, Audi began using two diagnostic connectors. They're mounted under the driver's-side footwell area and are black on the left, brown on the right. The black connector has ignition key-on voltage on the top terminal and is grounded on the bottom terminal. The brown connector has a wire on the bottom pin. This wire is the control unit's diagnostic output. Normally, a factory scan tool is used to get codes and cycle outputs. But you can still get codes out of the diagnostic connectors with the same tool used on Audi 80 and 90 models. A jumper wire spliced to one side of an LED bulb and a 330-ohm, 1/4-watt resistor spliced to the other side can be placed between the positive terminal of the left diagnostic connector and the control unit's output terminal, in the right connector. To initiate the code sequence, the control unit's output terminal needs to be jumped to ground for 4 seconds. Then just follow the same diagnostic procedures as in previous years.

On the 200 and 200 Quattro models, there are three diagnostic connectors. A white connector was added to the right side of both connectors. In the top pin of this connector is the control unit's diagnostic output wire, so this is where the ground side end of the LED test light goes. The bottom terminal of the brown connector is still the wire you need to tap to ground for 4 seconds to initiate code output.

In 1990, the diagnostic connectors on the Audi V8 Quattro were moved to the passenger-side footwell area, below the auxiliary relay panel, and another yellow diagnostic connector was added for good measure. For once, California techs got lucky. All you had to do was jumper the two lower pins of the two connectors on the left to get codes to flash out from the CEL. On federal vehicles, this may not work. So pull out your LED test light again and connect both leads between the two top terminals of the two outermost connectors (the black connector on the left and the new yellow connector on the right). During this retrieval sequence, the transmission gear position indicator is on. This means you're in "limp-home" mode. If the engine isn't running, you'll get a code 2111 (engine speed sensor) because of the lack of a speed signal, which is normal.

Audi changed the location of the three diagnostic connectors on 100 and 200 series cars in '92 to the underhood relay panel in the cowl area, on the driver's side. The diagnostic procedure stayed the same, though.

In '95 Audi made still more changes. The 100 and 200 were replaced with the S-series sedan, which maintained the previous diagnostic system. However, the A-series received OBD II treatment. The test connectors are still there for Audi's proprietary scan tool, but that's all they're good for. All other models, meanwhile, lost the ability to give us codes without expensive tools.

Generally, self-diagnostics can always be performed while the engine is running, and a spirited test drive is encouraged, especially with turbo models to check the boost sensor. This is kind of like a Ford KOER test or a Nissan Mode 5 test. A wiggle test also comes in handy to help duplicate the conditions under which a fault was set.


BMW started using self-diagnostics on its 1987 vehicles, and their method of doing things is much simpler than Audi's. To set things in motion, just perform five full-throttle applications within 5 seconds and any one of four one-digit codes will blink out on the CEL. Because the ECU's wakeup call is initiated by the wide-open throttle switch, that's obviously the first thing to check if you can't go into self-diagnostics. Note that M-series cars did not posses this form of self-diagnostics until '92, when the M5 had its engine slightly enlarged from a 3.5 to a 3.6 DOHC.

Things stayed pretty much the same until the '88 735 model, which added four-digit codes along with data stream information through the use of a factory MoDic tester. Of course, with more codes came more work. In order to activate the next code, you have to step on the throttle for 10 seconds.

This differs slightly from the '88 750iL. This car has a V12 engine, which is treated like two inline 6-cylinders in that BMW uses two separate control units. These control units have their own codes, and getting them to come up is done the same way-with five WOT applications. The right bank of cylinders will display codes first. (You can tell because all the codes start with one flash.) To get the left bank of codes, just hit the gas pedal six times. You'll know you've done it right because all these codes will start with two flashes. To clear codes, simply unplug the applicable control unit for at least 10 seconds.


In 1984, Mercedes-Benz began using a form of self-diagnostics on its 190E model. This basically involved checking the feedback signal from the oxygen sensor to the control unit through a diagnostic socket located on the driv-er's-side inner fender. A duty cycle meter, or a scope that indicates duty cycle, can be plugged into pin 3 of this diagnostic socket while the engine idles. If everything is working correctly, you should get a duty cycle of about 50% with some movement while revving the motor. However, if the duty cycle does not change but stays at a fixed percentage, that indicates that a fault is present. Each fault has its own default percentage between 0% and 100%. All other Mercedes models got the same self-diagnostic system two years later, in '86.

In 1989, Mercedes' California vehicles received an additional diagnostic connector near the battery. This one has a push button in the No. 2 position and an LED in the No. 4 position to access codes, as required by California law. With the ignition key on, just push the button in for 2 to 4 seconds and watch the LED blink out a code from 1 through 10. Pushing the button again displays the next code and so on, or the LED will stay lit if no codes are present. If there are no codes in memory, the LED will flash once. Hitting the button again for 2 to 4 seconds now allows the control unit to switch into duty cycle feedback testing.

To clear codes, you must display them first, then, after 2 seconds, hold the push button down for 6 seconds. You must do this after every code retrieved. If you have a federal model with this diagnostic plug, you can still get codes even though you don't have a push button or an LED. Just jumper pin 3 to ground for 2 to 4 seconds and the CEL should spit out codes. To clear the codes, jumper pin 3 to ground for 6 seconds for each code, just like on California models.

In '92, on some newer Mercedes models like the 400E, a different diagnostic connector is used that requires an adapter to connect a duty cycle meter for percent testing, but California models still maintain the push button and the LED.


Volvo started using its diagnostic routine on 1988 700 series models, and on the 900 series when it came out in '89. Volvo may have taken a long time to get into the game, but all that planning was time well spent because they provided a self-diagnostic system that's easy to use and has grown as more complex systems have been added.

Three diagnostic modes are available to help diagnose problems: Mode I allows you to get codes stored in memory. Mode II requires you to cycle various inputs to the ECU and puts out a code if the ECU notices a problem. Mode III is an output state check that cycles various outputs.

The diagnostic connector is found behind the driver's-side strut tower. It has a push button, an LED, a pigtail wire and six sockets, numbered 1-3 on one side and 5-7 on the other. Since this engine management system has two control units-one for the ignition and one for fuel injection-codes must be extracted separately. To pull fuel injection codes, put the pigtail into socket No. 2 and turn the ignition on. Then push the button on the connector down for 1 second. The LED will start to blink out a three-digit code. If you hit the button one more time, it will blink out the next code, if there is one, or repeat the first code.

That's all it takes to get codes. To clear them, push the button down for 5 seconds and, when the LED lights, hold it for another 5 seconds. After this, you should get only a 111, which signifies that no problems are present.

To get into mode II, put the pigtail into socket No. 2, turn the ignition on and push the button twice for 1 second each time. Now you're into the input state check, and the LED will start to flash quickly. When you step on the accelerator and the throttle switch comes off idle, the LED will flash out a code 332. If you activate the WOT switch, you'll get a code 333. Crank the engine and you'll get code 331. A/C request, gear select and a/c compressor are some of the other inputs you can check. Others were added later.

To activate mode III, push the button down three times for 1 second each. Now the ECU will cycle the outputs one at a time. The injectors and idle control valve should pulse, while the purge solenoid and cold start valve should click. Most of these outputs will cycle between 3 and 10 seconds, depending on the year and model of the vehicle.

To get ignition system codes, follow the same procedures, but this time plug the pigtail into socket No. 6. In mode I you'll get codes, in mode II you'll test the throttle switch and crank sensor inputs and in mode III you'll cycle the EGR controller.

In '92, Volvo introduced the 800 series, and while the same basic procedures were followed, some subtle changes were made to the system. First, there were now two diagnostic connectors (A and B) mounted behind the driver's-side headlight. Use connector A, sockets Nos. 2 and 6 for fuel injection and ignition system self-diagnostics. On '93 models, when going into mode III (output state check), you must unplug three injectors to get it to go through the test.

Volvo added another feature on '93 models-a fourth mode. Mode IV is used to individually cycle the outputs by inputting a code. This can be done only with the pigtail in socket No. 2, for fuel injection testing. After pushing the button four times, the LED will use one long flash to prompt you to input a code. Enter the first number of the three-digit code you're going to enter by pushing the button that many times. The LED will give you another long flash. Then enter the second number the same way. Finally, enter the third number after the third long flash. The LED will then repeat the code you just input and proceed to cycle that output. However, you must go into modes I and III first, otherwise the ECU thinks it's communicating with a scan tool.

Note that you can change the rate of mode IV by entering a code 311 for normal speed, or 312 for double speed. A code 313 will get you into 10X speed, for scan tool communication.


Ten years before Volkswagen rereleased the Beetle, its first self-diagnostic system was just getting started in California. In 1989, VW eliminated it, circa TSB No. 89 02. Some '88s have their self-diagnostics disabled. These ECUs will have a yellow sticker on them. On vehicles built before January '89, you can get codes out of a Digifant I-equipped California vehicle if the Check Engine light is on.

Getting codes is a fairly straightforward procedure: With the ignition on, depress the Check switch on the dash for 4 seconds and the CEL will flash out a four-digit code. To display the next fault code, repeat the previous step. Repeat this procedure until the CEL flashes on and off for 2-1/2 seconds each time, just like on an Audi. If no problems are found, you'll get a code 4444. To clear codes you must disconnect the CTS, hold the Check switch down, turn on the ignition for 5 seconds, then turn it off.

On CIS-equipped Volkswagens, you can get codes out of the knock sensor control unit, as well. Just pull out your LED jumper or logic probe and connect it between the diagnostic test pin in the harness going to the distributor and the positive battery terminal. The LED should light if the control unit is powered up. Next, start the engine and accelerate over 3000 rpm. The LED should go out. If it doesn't, there's a fault.

Tap the same diagnostic lead you're using to ground for 3 seconds and one of seven four-digit codes will blink. To get the next code, repeat the previous step. Note that the memory will be erased every time you turn off the ignition.

You may find Audi-style diagnostic connectors under the dash on '89 model Volkswagens. You can use them to pull codes just like on a late-'89 Audi model, except they are black and white, not black and brown. Be aware that the power and ground terminals may be switched on the black plug, so check polarity before attempting anything. Also, this is not a factory-recommended procedure, and I did not always get the code I set during testing. Sometimes I got no response. This also applies to 1990 and later Corrado models, where the diagnostic connector is located under the shift boot. In these cases, use only the black and white plug, not the blue.

On 1990 Jettas, Golf GTIs, Foxs and Passats, you can pull codes using the black, white and blue diagnostic connectors. One end of your LED test light goes to the top of the black connector, the other goes to the top of the blue connector. To start the code output sequence, jumper the bottom terminal of the black plug to the bottom pin of the white plug for 4 seconds. Repeat this to get more codes, until you get a consistent 21�2-second on/off flash, indicating no more codes.

By 1991, Volkswagen included its own jumper assembly under the carpet in the trunk or in the glove box, to jumper between the black and white connectors. Follow the same procedures as outlined above. To erase codes, connect the jumper provided, then turn the ignition on and remove it after 21�2 seconds. You should get a code 4444, for no faults. After repairs have been made, you'll have to reset the adaptive strategy of the ECU. To do it, disconnect and block the crankcase vent hose, then start the engine. Next, unplug the CTS and leave the connector off for 1 minute. Then reconnect it, but only if the cooling fan is off. You can now shut down the engine and put the vent hose back on. To finish things up, clear the CTS code you just set.

On '92 Volkswagen Corrados, the two diagnostic connectors are right under the heater controls, either behind some blockout caps or under the shift boot. Once again, you can use a jumper wire on the bottom two pins for 4 seconds to pull codes. The CEL will flash on, confirming that things are working. You'll also get codes 2111 and 2113 (for the cam and crank sensors) if the engine is not running. If it is running, you must keep engine rpm below 1300.

Self-diagnostics were made available on all other Volkswagen models in 1992, and they include an output state check, like Audi's. You can cycle several different outputs, but only in one sequence. To perform the function, connect the jumper, turn the ignition on and after 5 seconds, unplug the jumper. Then step on the accelerator to turn on the component. A code pertaining to the component being activated will then flash out. Keep plugging in the connector for 4 seconds to cycle through all the outputs, then step on the throttle to activate them individually. Note that if you exit in the middle of this sequence, the computer will remember, and pick up at that same point when you go back in. After pulling codes and checking the outputs, you can now go in and clear all applicable DTCs. After you get to the end of the code sequence, the CEL should flash for 2-1/2-second intervals. At this point, just install the jumper for 4 seconds and the codes are cleared.

Things changed slightly in '94, when Volkswagen switched to one diagnostic connector-in the center console under the heater controls. All models were also provided with an OBD I connector plug to do the jumping. Of course, you can still use a jumper wire between pins 4 (ground) and 15 (ECU output) and go through the same diagnostic procedure as you would on any Volkswagen. And that's that-until OBD II changed the rules of the game forever!