TRW MPS (TYPE 1) - System Overview
A far from bland coloured box, this Red & Yellow ECU is instantly recognizable. It is one of the earliest TRW Airbag systems and had no internal impact sensors relying instead on two external sensors mounted directly behind each headlamp on the inner wings. Whilst the ECU itself may be buried anywhere in the vehicle these sensors are easy to spot especially as they are always either bright Yellow or Orange. Indeed the wiring of the entire Airbag system is independent to the vehicle and covered in bright yellow flexible conduit or tape to specifically denote its usage from other wiring as a safety related matter. Looking for these sensors is the easiest way to determine if a vehicle built in 1996 when this system was replaced across the entire model range, has this ECU or the TRW SPS1 which replaced it. Although in all other countries this ECU was changed to the later SPS type 1, it seems that North American Range Rovers (P38), continued to have it fitted until 1999. The MPS designation is in respect of Multi Point Sensing.
SM011 - TRW MPS (TYPE 1) - System Help file
Version 1.26

TRW MPS (TYPE 1) - Known Fitments
Vehicle makes, models and variants known or believed to be using this vehicle system, required diagnostic lead and degree of known compatibility.

Vehicle Make Vehicle Model Vehicle Variant Diagnostic Lead
Land Rover Range Rover MK I (Classic) 1994> Green Airbag Lead
Land Rover Discovery < 1996 Green Airbag Lead
Land Rover Range Rover MK II (P38) (non NAS) < 1996 Black OBDII Lead
Land Rover Range Rover MK II (P38) NAS ONLY <1999 Black OBDII Lead
Rover Rover 800 < 1996 Black OBDII Lead

TRW MPS (TYPE 1) - Physical Details

TRW MPS (TYPE 1) - Pin Outs
Details of the pin usage for the ECU connector(s).

 
1 Engine Compartment Fusebox
2, 3 Not Used
4, 5 Not Known
6 Not Used
7, 8 Not Known
9 Data Link Connector
10 Not Known
11 Data Link Connector NAS
12 BECM
13 Ground
14 Instrument Cluster
15 Not Known
16, 17 Drivers Airbag via Rotary Coupler
18 Not Known
19 Not Used
20 Data Link Connector NAS
21 Not Used
22 Instrument Cluster
23, 24 Not Known
25 Not Used
26, 27 Not Known
28, 29 Not Used

SM011 - TRW MPS (TYPE 1) - Diagnostic Capabilities (Read Fault Codes)
The MPS airbag system can self detect up to 24 faults. Most of these are major or safety related faults causing full system shutdown with only a few being minor caused by, for instance, a flat battery. The systems perform a self-diagnostic test that takes about 15 seconds whenever the ignition is switched on, logging any faults that are found, then at regular intervals thereafter. Resistors are placed at strategic points in the airbag wiring harness / loom giving the systems the ability to self detect open or short circuits. Main loom loops are from the ECU up the column through the spiral cassette through the airbag and back through the spiral cassette to the ECU; from the ECU through the passenger airbag and back again; on MPS systems, one through each of the two crash sensors mounted behind the head lamps at the front and then returning to the ECU, then two loops each going to the instrument cluster, through a bulb each and back again. In accordance with the manuals, no repairs must be carried out on the loom at all; hence, no wiring diagram is supplied in the manufacturer's manuals. All problems involving the airbags, spiral cassette, crash sensors, or loom must be done in strict accordance with the relevant manufacturer's workshop manual instructions. There is a deep memory within the airbag ECU that keeps a long-term record of resets to detected faults. This means that if a particular connection was poor and went open circuit - even just once - the fault would be logged by the system as "a sensor is open circuit" and the airbag warning light would come on. If the fault was not found and the fault code memory was cleared it would be very likely to reappear. This would be logged as an intermittent fault within the system.

SM011 - TRW MPS (TYPE 1) - Diagnostic Capabilities (Clear Fault Codes)
This function checks the fault code memory for resident faults and clears the fault code memory if the fault has been rectified. Having deleted the faults the system then rechecks the fault memory to ensure that it is clear. Failure to clear the fault memory successfully is usually due to the system re-logging the fault the moment the fault memory is clear, meaning that the fault has not been rectified properly and as far as the system is concerned, still exists. The system may also carry out a re-check for successful clearing of the fault code memory but then the system may re-log the fault shortly after.

SM011 - TRW MPS (TYPE 1) - Diagnostic Capabilities (Settings)
Values, configuration settings, and other stored information which can be read from the ECU, edited and then rewritten back. Read settings can also be stored as a standard HTML page for reference. These pages can then later be re loaded and re written back to the ECU. Please note that some values may be read only due to the fact that they are supplied from the ECUís ROM or are internally calculated.

The SRS airbag has only one programmable option:
  • VIN: The electronically stored Vehicle Identification Number (VIN) in this airbag ECU. This number should be changed if the ECU is fitted in another vehicle. It should also be entered on new airbag ECU's. The number can be found on the VIN plate under the bonnet or on the visible VIN tag at the bottom of the windscreen.
Other information that can be read from the airbag ECU:
  • Manufacturer: Gives the manufacturer's name for the airbag ECU.
  • Model: Gives the manufacturer's model code allocated to this airbag ECU. Not all ECU types feature this information diagnostically.
  • Software version: Gives the software version number for this airbag ECU. Not all ECU types feature this information diagnostically.
  • Hardware version: Gives the hardware version number for this airbag ECU. Not all ECU types feature this information diagnostically.
  • Serial number: The electronically stored serial number for this airbag ECU, and can be found printed on a label affixed to the top or side of the ECU.
  • Date of build: Gives the electronically stored date of build for this airbag ECU. Not all ECU types feature this information diagnostically.
  • Part number: Gives the vehicle part number for this airbag ECU. Not all ECU types feature this information diagnostically.
  • Part reference: Gives the part reference which identifies the family variant of this airbag ECU. Not all ECU types feature this information diagnostically.
  • Driver's airbag/Passenger's airbag: This denotes fitment or omission of the driver's/passenger's airbag. Not all ECU types feature this information diagnostically.
  • Right hand pretensioner/Left hand pretensioner: This denotes fitment or omission of the right hand/left hand seat belt pretensioner. Not all ECU types feature this information diagnostically.
  • Driver's side airbag / Passenger's side airbag: This denotes fitment or omission of the driver's/passenger's side airbag. Not all ECU types feature this information diagnostically.
  • System type: Some airbag ECU's / DCU's are fitted in different vehicle models. Where this is the case this value shows which system has been detected. Where the ECU / DCU type is unique to a vehicle model, this value then indicates the vehicle model.