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Problems

Blocked heater fresh air inlet drain hose

Both Bosch Motronic and Siemens engine management ECUs suffer water damage due to blocked heater fresh air inlet drain hose. This hose is triangular in shape and is intended to drain any water which collects in fresh air inlet. Leaves and other debris block this hose which allows water to build up eventually flooding ECU compartment and causing ECU failure. The fix is easy – shorten hose by 2cm at bottom with snips + clear drain pipe with thin wire as part of winter service. If your ECU has water staining, please click here for fast low-cost ECU inspection service.

Bosch Motronic engine management ECU

MOST BMW models are fitted with Bosch Motronic engine management ECUs which suffer from common ignition failures. Bosch Motronic ECUs are also fitted to Alfa Romeo, Peugeot and Vauxhall (GM) cars from 1986 to date. TO PROCEED – It is important to count the number of ECU pins to correctly identify next page. Please click HERE for photos of these ECUs to assist identification. (Bosch identify their Motronic part numbers with prefix – 0261 20X XXX)

Bosch Motronic with 35 pin (2 rows) or 55 pin (3 rows) connector

 

Bosch Motronic common failure symptoms
(35 & 55 pin ECUs)

Bosch Motronic engine management ECUs with integral ignition power stage are increasingly suffering failure as ECUs age. These ECUs are commonly fitted to Alfa Romeo, BMW and Vauxhall(GM) cars from 1987 up to the introduction of distributorLESS systems. Click here to see photo of ECU.

To identify Motronics with integral ignition power stage look at the underneath of the ECU. There are 2 small screws (Philips or Torx head) which locate the connector body to the ECU base plate and either 2 or 4 larger screws (Philips or Torx head). ECUs with 4 larger screws have integral ignition power stage – if 2 of the larger screw holes are blanked off with plastic plugs then there is a separate ignition power module(s) and THIS PAGE DOES NOT APPLY – THERE IS A SEPARATE IGNITION AMPLIFIER LOCATED IN ENGINE COMPARTMENT. Click here to see photo of ECU. NOTE:Bosch Motronic ECUs with 35 pins fitted to Peugeot or Citroen cars (up to 1992) do NOT have integral ignition amplifier – there is an ignition amplifier module located below inlet manifold and this is the most likely cause of loss of spark on 2 cylinders on these 2 particular makes.

Symptoms

1) Car breaks down (sometimes without warning) – apparent loss of spark and NO fault codes.
2) There may be a history of intermittent starting or misfire problems but note below for Vauxhall cars.

Diagnostic Checklist

ALL VAUXHALL CARS with this system – REPLACE large fuel injection relay for vehicle non start or running problems – before condemning anything else!

1) Check that injectors and fuel pump are working normally.
2) If yes, check for very low ignition pulse – very weak spark sometimes visible.
3) If yes, check all LT and HT connections for defects and exchange coil if available.
4) If above OK then ECU confirmed failed.

If in doubt about whether ECU is cause of problem on your car, try our low-cost ECU inspection service. This is fast, low-cost and many Motronic ECUs with this common problem can be fixed during inspection – avoiding costs of rebuild.

DO NOT REMOVE ECU COVER – THESE ECUs FEATURE HIGHLY SENSITIVE MICROELECTRONIC INTEGRATED CIRCUITS THAT CAN BE DAMAGED BY NORMAL ENVIRONMENTAL ELECTROSTATIC CHARGES.

For Bosch Motronic with 88 pin (3 row) connector

There are many failures of Bosch Motronic DIS (Direct or Distributorless Ignition System) ECUs commonly fitted to Alfa Romeo, BMW and 4 cylinder Peugeot cars from about 1992 onwards. Click here to see photo of this ECU.

Part numbers are 0261 20X 4XX/5XX/others. The system fitted to 4 cylinder Alfa Romeo and 6 cylinder BMW cars is ‘coil per cylinder’ system whilst that fitted to 4 cylinder Peugeot is a twin coil ‘wasted spark’ system. Click here to see photo of the 88 pin Bosch Motronic for accurate identification. (It is important not to confuse this system with earlier Peugeot and Citroen cars which use 35 and 55 pin Motronic ECUs.)

Symptoms

1) Misfire on one (or more) cylinders (Alfa and BMW), or no spark on 2 cylinders for systems fitted to 4 cylinder Peugeot.

Diagnostic Checklist

1) ECU failures so far have been associated with coil pack failure which can be confirmed by VERY close visual inspection of coil pack – look for split in coil casing or burn marks. All the evidence we have seen indicates that coil pack failure guarantees ECU failure.
2) If possible, check for severly reduced coil KV on effected cylinders. A very weak pulse can sometimes be detected.
3) Do not confuse this system with earlier 35 and 55 pin Motronic systems fitted to some Peugeot and Citroen cars. These earlier systems had separate ignition amplifiers mounted in the engine compartment. Refer to ECU photographs HERE to get ECU identification right.

DO NOT FIT REPAIRED OR NEW ECU UNTIL NEW COIL(S) IS FITTED

If in doubt about whether ECU is cause of problem on your car, try our low-cost ECU inspection service. This is fast, cheap and many Motronic ECUs with this common problem can be fixed during inspection – avoiding costs of rebuild.

DO NOT REMOVE ECU COVER – THESE ECUs FEATURE HIGHLY SENSITIVE MICROELECTRONIC INTEGRATED CIRCUITS THAT CAN BE DAMAGED BY NORMAL ENVIRONMENTAL ELECTROSTATIC CHARGES.