Background

The ECU controlling the engine management on 24V Carltons and Senators is manufactured by Bosch and designated Motronic M1.5. The system fitted on latter 12V catalysist equipped cars is also call Motronic M1.5. The two differ slightly, the 12V system does not utilise knock sensors but still controls the ignition timing.

The ECU is situated under the drivers side kick panel, to remove you need to loosen the door seal, remove the plastic trim, and unscrew the three securing bolts(8mm hex head), this will give you enough room to disconnect the multi-way connector (with it's locking mechanism) and remove the ECU from the car. You can usually tell if the ECU has been removed before as from the factory they have a plastic sheet to deflect any water from as leaking windscreen (see image above) this is attached with a piece of masking tape!

Trouble shooting the Motronic M1.5 ECU

The following downloadable <ecu15.pdf> file was produced by Peter Kay (another Autobahnstormer!) and shows the electrical connections between the ECU and it's sensors and actuators. It covers how to read trouble codes in detail. Many thanks to Peter for allowing it's reproduction here. It was originally to be published in SSN (Straight Six News) the quarterly magazine of the Autobahnstormers.

As described in Peter's article if the ECU light () should illuminate you can read the trouble code(s) by shorting pins A and B of the ALDL socket under the bonnet. The ECU light will then flash the code out three times. It will flash "12" out first, then the trouble code(s).

The code(s) can also be read by using the hand-held GM Tech 1 diagnostic tool.

Use the table below to find out what the ECU thinks is wrong, what causes the fault and what the ECU does to compensate it. I suggest you then use Peter's diagram to find a measure the signal yourself with a DVM. Most faults are cause by dirty connectors / wiring breaks and these should be checked if the signal at the sensor under question is present and correct. Remember to check the power and ground connections to the sensor as well! The ground connections to the inlet manifold have also been known to cause problem and so these should also be cleaned and checked.

Code Diagnosis Description 13 O2 SENSOR OPEN CIRCUIT Cause Over a period of t>3s the Oxygen sensor voltage is 0.63 > Us > 0.38V Result  ECU uses 0.45V as input   14 COOLANT TEMP. VOLTAGE LOW Cause Engine temperature > 140ºC Result Value of 80ºC used (or if air intake temp < 0.4ºC and engine been running less that 3mins, air temp taken as replacement) 15 COOLANT TEMP. VOLTAGE HIGH Cause Engine temperature < -35.4ºC and Air temperature < -20ºC  Result Value of 80ºC used (or if air intake temp < 0.4ºC and engine been running less that 3 minutes, air temp taken as replacement) 16  KNOCK SIGNAL (Circuit 1) Cause Engine > 85ºC and Unrecognised knock signal from sensor 1 for more than 10s with engine above 2000rpm. Result Ignition timing retarded by 12º 17 KNOCK SIGNAL (Circuit 2) Cause Engine > 85ºC and Unrecognised knock signal from sensor 2 for more than 10s with engine above 2000rpm. Result Ignition timing retarded by 12º 18 KNOCK CONTROL UNIT Cause Engine > 85ºC and Unrecognised knock signal for more than 10s with engine above 2000rpm. Result Ignition timing retarded by 12º 19 INCORRECT RPM SIGNAL Cause Engine speed signal is interrupted > 2000rpm 21 THROTTLE POSITION SENSOR VOLTAGE HIGH Cause Throttle valve potentiometer voltage > 4.95V Result Replacement value is calculated from air flow meter signal and rpm 22 THROTTLE POSITION SENSOR VOLTAGE LOW Cause Throttle valve potentiometer voltage < 0.1V Result Replacement value is calculated from air flow meter signal and rpm 23 KNOCK CONTROL MODULE; REPLACE ECU Cause Unrecognised knock signal for more than 3s with engine above 3500rpm. Result Ignition timing retarded by 12º 25 INJECTOR BANK 1 VOLTAGE HIGH Cause Short circuit to battery voltage 31 NO ENGINE RPM SIGNAL Cause Ignition ON No rpm signal NB. Always present with engine off! 38 or 44 O2 SENSOR CIRCUIT VOLTAGE LOW Cause Oxygen sensor voltage < 0.09V for t>2.6s Result  ECU uses 0.45V as input 39 or 45 O2 SENSOR CIRCUIT VOLTAGE HIGH Cause Oxygen sensor voltage > 1.099V for t>2.6s Result  ECU uses 0.45V as input 48 BATTERY VOLTAGE LOW Cause Battery voltage < 10V for t > 3min Result No block learning and some compensation for low voltage 49 BATTERY VOLTAGE HIGH Cause Battery voltage > 16V Result No block learning and some compensation for high voltage 52 CHECK LIGHT VOLTAGE HIGH Cause Short circuit to battery voltage 53 FUEL PUMP RELAY VOLTAGE LOW Cause Short circuit to GND or interruption 54 FUEL PUMP RELAY VOLTAGE HIGH Cause Short circuit to battery voltage 55 REPLACE ECU Cause ECU fault 56 IDLE AIR CONTROL VOLTAGE HIGH Cause Short circuit to battery voltage 57 IDLE AIR CONTROL VOLTAGE LOW Cause Short circuit to GND or interruption 61 FUEL TANK VENT. VALVE VOLTAGE LOW Cause Short circuit to GND 62 FUEL TANK VENT. VALVE VOLTAGE HIGH Cause Short circuit to battery voltage 63 DUAL RAM VALVE VOLTAGE HIGH Cause Short circuit to battery voltage 65 IDLE CO POT. VOLTAGE LOW Cause Potentiometer voltage < 0.25V NB. Not used with Catalytic converter. 66 IDLE CO POT. VOLTAGE HIGH Cause Potentiometer voltage > 4.81V NB. Not used with Catalytic converter. 69 INTAKE AIR TEMP. VOLTAGE LOW Cause Intake air temperature calculated to be > 140.3ºC Result 19.9ºC used 71 INTAKE AIR TEMP. VOLTAGE HIGH Cause Intake air temperature calculated to be < -35.4ºC Engine running for > 3min Engine at idle rpm for 10s Result 19.9ºC used 73 AIR FLOW SENSOR VOLTAGE LOW Cause Engine rpm > 1000rpm Air flow meter signal < 0.15V Result Replacement value calculated from rpm and throttle plate position 74 AIR FLOW SENSOR VOLTAGE HIGH Cause Air flow meter signal > 4.9V Result Replacement value calculated from rpm and throttle plate position 75 TORQUE CONTROL VOLTAGE LOW Cause Vehicle running, PWM signal for > 2.56s, period < 8ms or > 12ms NB. Only applicable on automatics 81 INJECTOR BANK 1 VOLTAGE LOW Cause Short circuit to ground or lead interruption 87 A/C CUTOFF RELAY VOLTAGE LOW Cause Short circuit to GND 88 A/C CUTOFF RELAY VOLTAGE HIGH Cause Short circuit to battery voltage 93 HALL SENSOR VOLTAGE LOW Cause Short circuit to GND 94 HALL SENSOR VOLTAGE HIGH Cause Short circuit to battery voltage

A detailed look into the ECU

The Motronic M1.5 ECU has a 55pin connector and the heart of the system is a Siemens 80515 microprocessor with 8k embedded ROM. Additional firmware and the various "maps" are located on an adjacent 27C256 EPROM . A datasheet for the 80515 family of processor can be downloaded here <m80515.pdf>, a typical EPROM (27C256) datasheet can be downloaded here <am27c256.pdf>.

As mentioned earlier, there are two types of M1.5 ECU used on club cars, one with knock sensors (24v engines) and one without (12v engines). These are identified by part numbers (0 261 200 356, 24v engines, 0 261 200 366, 12v engines) and ECU Version Indents (FZ for 24v and GK for 12v)

24v engines: Motronic M1.5 with knock detection

12v engines: Motronic M1.5 without knock detection (note knock sensor filter board is not present)

Although I haven't tried it, the rarer 12v unit can probably be replaced with a 24v unit with the correct firmware, you might need to remove the knock sensor filter PCB, but otherwise the board look like they are identical, the 12v board has holes ready to accept the knock PCB.

The firmware (affectionately known as the CHIP!)

The firmware has undergone a number of revisions over the cars life. Coded into each binary is both a Bosch number, a Vauxhall/Opel part number and the ECU version identification. The control maps are stored in different locations in each version. The following is a table of the firmware versions I have found and the car model they were in.

Depending on the age of the ECU/car the firmware EPROM is either located in a locking 28pin socket or soldered directly onto the PCB. If you are thinking for changing the EPROM and 'chipping' your car you might need to de-solder the original EPROM and solder in a socket. Instructions for doing this job can be found here but I stress it easy to destroy an ECU if done incorrectly and I hold take no responsibly for your actions if you end up destroying it!

Inside the firmware (Maps)

There are 4 main fuel and 4 main ignition maps. These are selected by a combination of load, revs and throttle position. The maps shown below have been extracted from the latest firmware, Bosch code 1 267 357 042. I am indebted to LandShark in the USA for helping in their location. Outside Bosch he and his colleague are probably the only people who how how Motronic really works as they have reverse engineered the the system in many BMWs. The maps were not radically changed in any of the software versions I have obtained, just a few tweaks here and these.

There are 4 main part throttle ignition maps:

and 4 main part throttle fuel maps:

There are 3 main WOT ignition maps:

There are 2 main WOT fuel maps:

MkIII remapped fuel and ignition maps. All the above maps were smoothed and altered to creater a much more enjoyable driving experience.

The last five are interesting. You can see that the load index isn't really used in these fuel maps, and so the input from the air-flow meter is disregarded during WOT acceleration. The ECU also goes into open loop in such situations so there is no oxygen sensor input. Therefore the ECU has no way of knowing about any nice straight through exhaust you have fitted to improve the air-flow, or nice performance air-filters...not to mention expensive gas-flowed cylinder head. At part throttle the air-flow meter will be measuring such breathing improvements, and anyway the oxygen sensor will be holding the mixture around stichometric most of the time. But to match the improved breathing with more fuel at WOT these are the two you need to tweak.

Irmscher 4.0L 24v

The Irmscher 4.0L engine is infact almost a completely different engine, with a new cast block (complete with C40SE embossed into it) new crank, con-rods, pistons cylinder head. The only 'electrical' change is infact the fitting of increased flow fuel injectors and a different air flow meter.