Component Identity

SM Steering Module

MR Main relay

FPR Fuel Pump relay

BATT Battery

IS Ignition switch

FP Fuel Pump

EAV Extra air valve

AFM Air flow meter

PR Power resistors

Operation

The white (W) wire from the ignition switch supplies power through the right hand diode in the Steering Module (terminals 4 to 1) seen above. From there it connects to terminal 85 of the Main relay, through the relay windings to earth via terminal 86 to close the contacts when energised.

Power is now available directly from the battery via terminals 30/51 and 87 to the air flow meter (Fuel Pump contacts), Pin 10 of the ECU and to the Power Resistors which connect to the fuel injectors. However, current can only energise the injectors when the ECU completes their circuits to earth with appropriately timed injection pulses.

The Fuel Pump relay is also activated through the Steering Module but in two different modes. Initially, in engine cranking mode, power is available to the Steering Module terminal 3 via the white/red (WR) wire from the ignition switch cranking circuit. Then, as the engine starts, in engine running mode, power reaches terminal 2 via the blue/purple (UP) wire coming from the now closed Fuel Pump contacts inside the Air Flow Meter, also connected to Pin 20 of the ECU.

In either mode, current passes from the Steering Module via the respective diodes at terminal 5 to the Fuel Pump relay terminal 85, through the relay windings to earth. The closed relay contacts operate both the Fuel Pump and the Extra Air Valve with power drawn from the ignition switch.

These two diodes, by their nature of preventing current from flowing in the reverse direction, ensure that operating current from terminal 3 cannot pass to terminal 2 and vice versa.

In summary, the Fuel Pump is initially energised in the cranking mode but as soon as the engine draws air through the air flow meter its internal Fuel Pump contacts close, completing the alternative circuit to keep the Fuel Pump energised until either the ignition is switched off or the engine stalls, the Air Flow Meter flap closes, thus opening its internal Fuel Pump contacts.

The above operational description is limited to the immediate circuitry of the subject components but a complete Rover SD1 Efi circuit diagram can be viewed on the PDF available here:

Reliabilty and Replacement

Components in the Rover SD1 Efi System have varying degrees of reliability but the Steering Module has proved, over time, to be a very robust item not prone to chronic failure. One hears anecdotal evidence of failure but they seem to coincide with injudicious poking around with meter probes elsewhere in the system that cause short circuits capable of damaging the internal diodes.

The diodes, type 1N4006, are straight forward items readily available from semiconductor vendors at low cost and can be easily tested/replaced. However the fourth component in the module is an unusual fusible resistor, rated at 2.7 Ohms. Because it is an ECU protection and safety item it must be replaced "like for like". Replacements are inexpensive but will be harder to find.

To that end, and due to low failure rate, one often sees used Modules and Relays at Club Spares Days. Also SD1 Ebayers and Land/Range Rover S/H spares suppliers would readily provide them.

Conclusions

Because of its strange name and relative inaccessibility, the Steering Module and the associated relays have a reputation of unwarranted mysticism, whereas, in fact, it simply makes sure that the Main and Fuel Pump relays operate correctly and safely during the cranking and running modes.

Testing the Efi Steering Module, Main and Fuel Pump Relays by substitution is probably the quickest means of fault finding. However diagnostic tests are quite easy and will be posted in due course as a PDF here:

Please advise of errors and omissions.................................................Return to Efi Components Index