How to replace the ABS power unit on a P38

ABS brake problems are often down to failure of the power unit. The part is expensive, though quick to replace.

The ABS brake system on the P38A Range Rover is hydraulically power assisted and operated by the ABS power unit. This comprises an electrically driven pump, a pressure switch and an accumulator, and its job is to store hydraulic energy for the next braking application.

The ABS power unit’s electrically driven pump and pressure switch are both non-serviceable items, but the accumulator can be replaced. The accumulator, which is charged with nitrogen, can lose pressure with age until it no longer provides enough pressure to the brakes, often resulting in no pressure when you press the brake pedal.

But more often, it’s the electrical function of the pump itself that fails, so the whole assembly needs to be replaced. This is what had happened on the 2001 high-mileage Range Rover featured here, which eventually had no pedal pressure at all. The brakes themselves were found to be in good condition and the fault was traced to a failed ABS power unit. 

With the value of older second-generation P38A Range Rovers falling, the owner felt that fitting a new replacement ABS power unit, even at the lowest price of £600, was uneconomic. So he had sourced a secondhand unit which the workshop agreed to fit for him on the understanding that they were in no way responsible if the secondhand power unit did not work, or if it failed soon after it was fitted.

Using secondhand parts is always a risk, and we recommend using new brake components. The ABS power pump assembly is part number STC2783 (superseded to LR005953). Prices vary between £600 and £2000. Replacement is not difficult. Normally the brake system should be depressurised before working on it. This is done with the ignition switched off and pressing the brake pedal 30 times. After one minute, press the pedal another four times to ensure all the pressure is out of the system.

In our case, the system was already depressurised due to the fault, but we still advise going through the depressurisation procedure to avoid unexpected fluid release. Once the replacement ABS power pump has been fitted the brake system will, in most cases, need to be bled through the bleed valve on the side of the brake booster/ABS modulator.

Time: 1 hourCost: from £600Tools: General workshop tools, 10mm spanner and socket, 14mm spanner, hose clamp.

Thanks to : Maddison 4x4, Water House Farm, Station Road, Topcliffe, Thirsk, YO7 3SG. Tel: 01845 587407. Web: www.maddison4x4.com who did the work.

Health and safety

• The brake hydraulic system should be de-pressurised before working. • Always follow all health and safety precautions. Extreme caution should be taken when handling the accumulator that is attached to the power pump, as this is charged with nitrogen at a pressure of 80 bar. Do not puncture it or burn it. • When disconnecting and working with hydraulic components, wear eye protection in case of pressurised fluid escaping. • If in any doubt about the work or the condition of the system, ask a garage to check the components.

Click on the gallery below for our handy step-by-step guide…

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