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Lots of people like to claim that Range Rovers are too complex for the home mechanic to touch. This is far from the truth, as the Range Rover the the first vehicle I've owned that has seen me do anything more complex than change a spare tyre. However, there are limitations, but many of these can be overcome if you are determined enough and understand the limits.

For the most part, the Range Rover retains the meccano like construction of it's forbears. The 4.0 and 4.6 litre engines have increased piston diameter and stroke from the 3.5, but the engine is fundamentally the same design with a single chain driven camshaft. The addition of the GEMS engine management and the BeCM to control pretty much everything else does limit the home mechanics ability to undertake major work, but there is still plenty of scope for normal servicing and maintenance to save the cash for the garage bills when necessary.

Contents 1 Electronic Systems on the P38A 1.1 Engine Management 1.2 Gearbox and Transfer box 1.3 ABS and Traction Control 1.4 Airbags 1.5 HeVAC 1.6 Cruise Control 1.7 BeCM 1.8 Air Suspension (EAS) 2 Diagnostic Systems 3 Working without a Diagnostic System 3.1 So, how do I fix a problem 3.2 Intermittent Problems 3.3 Relays 3.4 BeCM Switching 3.5 Serial Links 3.6 CAN Bus 3.7 Electrical Troubleshooting Manual 3.8 SRS Wiring 4 ECU Repair 5 Battery and Charging 5.1 Replacing the battery 5.2 Not Starting or Charging

[edit] Electronic Systems on the P38A

[edit] Engine Management

Three different Engine Management systems were used on the P38A. All Diesel variants were equipped with the Bosch Electronic Diesel Control (EDC) system. Prior to 1999, V8 Engines used the Lucas/Sagem Generic Engine Management System (GEMS). From 1999 onwards, the newer engines used the Bosch Motronic 7.2.1 system, which provides some small performance improvements and better emissions control.

[edit] Gearbox and Transfer box

All diesel systems and the GEMS engine used the Bosch GS2.38.1 control ECU. Later (1999MY onwards) petrols used the newer GS 8.87.1 ECU. The newer ECU supports CAN bus connectivity to the Bosch Motronic Engine ECU, and also has improved adaptive control and some user visible changes like remembering if sport mode is set when you turn the ignition off.

The transfer box ECU is not connected to the diagnostic socket, so is of less interest to use here.

[edit] ABS and Traction Control

Traction Control, where fitted is also controled by the ABS ECU. Slightly different variants of the Wabco ECU were used on different model years.

[edit] Airbags

There are three generations of airbag control on the P38A. The earliest were the multi-point sensing systems, which can be identified by the yellow crash sensor wiring in the engine bay. These were used up to mid-1996. After that, the system was simplified to use a single sensor within the ECU. From 1999MY, seatbelt pre-tensioners and side airbags necessitated a new ECU.

The ECU is located under the centre console, close to the centre of the vehicle.

[edit] HeVAC

All models with climate control use the same Valeo ECU.

[edit] Cruise Control

The cruise control ECU lives within the dashboad. No diagnostic access is available prior to 1999MY.

[edit] BeCM

The BeCM has the same diagnostic interface across all the models. However, there are varying part numbers over the years, particular on earlier vehicles where there was a "low-line" and "high-line" variant.

Lots of specific information can be found on the BeCM page.

[edit] Air Suspension (EAS)

The EAS ECU was the same across the whole model range, and very similar to that used on the Classic. More information can be found on the P38A Suspension page.

[edit] Diagnostic Systems

Far and away the easiest way to access these systems is using a Diagnostic system like Rovacom Lite. Other, more expensive systems such as Land Rover's own T4 (aka Testbook) system are availble for professional use. The more expensive systems have no more features - in fact, some of them have less. All they offer for the extra money is ruggedized hardware for continuous workshop use.

You can get limited information from a simple OBD-2 scanner like the o­ne at http://www.obd-2.com which will allow you to see basic fault codes o­n the engine and power train. For the Range Rover order the ISO (red) cable at $122 including shipping world wide. I assume that the Testbook/Diagnos just use a superset of this protocol....

An interesting comparison to the Testbook is the software needed to control the LPG installation. The software and cables necessary to communicate with this system can be purchased easily and cheaply. I am sure that there is money to be made in producing a cheaper, PC based version of the Diagnos or Rovacom computers which are tied to a single vehicle to allow the home mechanic access to the same information.

However, o­ne very important thing to note is that a diagnostic computer is just a tool - like a hammer or a spanner. More accurately it's like a multi-meter. It can o­nly provide information to the operator that the operator can't see with their own eyes, based o­n electrical signals in the car. A friend relates a story of having his car hooked up to a Rovacom to diagnose a fault. The Rovacom reported error codes indicating failure of almost every single component in the air-con system. The actual fault turned out to be that there was a leak in the system and all the coolant had escaped - which was David's initial theory before taking the vehicle to the dealer.

[edit] Working without a Diagnostic System

Contrary to popular opinion, it's possible to do lots of these cars without the diagnostic systems. Typically, this means spending more time testing with a multi-meter, and possibly not being able to clear fault lights. This page includes some hints and tips on electrical troubleshooting and fixing on the P38A. Much of this information will also be applicable to any other vehicle.

First of all, to put any of this into practice you will need a good high resistance multimeter. My preference is for digital because it's easier to read, and all Digital Multimeters are inherently high resistance. Don't use a test bulb to check for continuity as the high current drain can destroy some of the sensitive electronics.

I went and got a good one from Maplin for about 30 quid. This provides a "hold" facility as well as a "max/min indication". I also bought a set of test probes to allow it to be hooked into place and, if necessary, the car taken for a drive to look for a max/min value at a particular location. It' also does up to 10A current reading and will locate live voltage in wiring without connecting anything.

The second thing that you'll need is to know how to use it to measure resistance, current, and voltage - and what these three things mean. See [HobbyElectronics] for a basic grounding in these quantites and how they are related by Ohm's Law.

Much of the electronics in the P38A is based on "ground path" switching - so you'll get a circuit with the +12V side connected to the relay/bulb/whatever to be powered and the switch (or switch side of the relay).

[edit] So, how do I fix a problem

First of all, don't panic. It's important to keep a clear head and approach any problem solving exercise in a logical and rational manner.

Secondly, try to isolate the problem as far as possible. If the wipers don't work on their intermittent settings, try the other settings and other interval settings.

Armed with this information, get your copy of the Electrical Troubleshooting Manual, a cup of coffee (or tea if you perfer), and sit down in the warm and spend some time working out exactly how it's supposed to work. What should you see? Going back to the wiper example, make sure you understand how the switch inputs are generated and what you sould see on each of the relevant input signals to the BeCM, and what outputs should switch in reaction. Work out where the connectors are located on the vehicle, and what voltages you should see under which circumstances.

Now that you have a knowledge of what's supposed to be happening, you can get out the meter and go and see if you can work out what is actually happening. The important thing is to try and isolate the problem - so in our wiper example, start by checking for continuity of the switch in each position, then checking for the same signal inputs to the BeCM, then checking the outputs, and finally checking the voltage reaches the components. Some people like to start in the middle and work out, but I recommend you start off being methodical in your approach and work logically down the wiring diagram in the ETM to isolate the cause. You'll learn a lot in the process, and when you progress to "middle out" approaches then you'll understand the short cuts you're taking.

Once you can see where something isn't happening as expected you can then do some more specific tests - for example, you see that a voltage isn't being switched at the BeCM, but the switch seems to be OK, you can you test the continuity of the wire between the two to confirm the fault location.

[edit] Intermittent Problems

These are always a pain to isolate. If the problem is intermittent, see if you can make it happen by moving wiring harnesses. It's also worth looking at fixing points and locations where wiring turns a sharp corner or goes through a grommet for signs of chafing.

[edit] Relays

Relays can be thought of as an electriccally operated switch. They allow a small switch, traditionally on the dashboard but often electronic in the P38A, to switch a much larger current. All the relays in the P38A are in the engine compartment fuse box.

[edit] BeCM Switching

One other thing you need to understand is that virtually every control inside the car is connected to the BeCM - so for example when you turn the headlight switch you are sending a request to the BeCM to turn the headlights on, and the BeCM will decide whether this should be done (ignition on) or not (ignition off).

[edit] Serial Links

A number of interfaces on modern cars are implemented using serial links. On the P38A they are usually a synchronous signal with three wires - direction, clock, and data. The vehicle ground serves as a common reference voltate for all three. An osciliscope is great for seeing exactly what signal is present, but you can still get a good idea from a voltmeter.

For example the signal from the RF remote receiver to the BeCM should normally show around 10V and you should see this fluctuate (lower) when you press the remote key buttons.

[edit] CAN Bus

From 1999MY the P38A introduces a CAN (Controller Area Network) between the engine management and auto gearbox ECUs). This is a two wire twisted pair. Each wire should have a reference voltage of +2.5V when idle. When data is transmitted one wire should fluctuate up to +3.5V and the other down to +1.5V. This permits much higher speed than the serial links and more reliable....

[edit] Electrical Troubleshooting Manual

You need the ETM to troubleshoot anything on this vehicle. Trust me.

[edit] SRS Wiring

SRS wiring is always enclosed in a protective yellow sheath (orange is used on some other Land Rover models). NEVER, EVER, EVER test SRS wiring in circuit unless you want an airbag in the face. See the P38A Interior page for more information on the SRS system.

[edit] ECU Repair

If you have ECU problems, Car Elecrronic Services, formerly owned by Rod Westbury, (www.carelect.demon.co.uk) offers an ECU rebuild/repair service, which has to be cheaper than a new ECU. His service covers the BeCM, GEMS ECU, HEVAC ECU, and the memory seat outstations. I'd be interested to hear from anyone who has used his service - I might need him o­ne day.

It is also possible to do your own DIY repairs on some systems, such as the BECM. While this might not be a guaranteed fix, it's often a worthwhile gamble.

[edit] Battery and Charging

All of this complex electronics isn't much good without the power in the system to run it!

[edit] Replacing the battery

If you are bemused by the array of technical trickery in the Range Rover, then you may be concerned (as I was) at removing the battery and what get's reset or confused.

• When removing the battery, open the bonnet, remove the battery cover, then lock and unlock the car with the remote and immediately remove the negative lead. This will stop the alarm going off because the battery has been removed.
• With no battery in the car, you will loose central locking and will be unable to open the tailgate. Go round and lock the doors manually, finally locking the driver's door with the key if you have to leave the car.
• When you come to replace the battery, unlock the driver's door, release the bonnet, and leave the drivers door open. Refit the battery, then put the key in the ignition to resynch the key to the car via the ignition transponder.
• You will then need to enter the radio code. You do know your radio code, don't you? If you enter it wrongly, switch the radio off and back on, then hold down the MODE button until the old code clears from the display and re-enter.
• You will also need to reset the electric windows and sunroof. For each one in turn, move the window through the full range of movement, twice. You will get "WINDOW NOT SET" and (e.g.) "LH FRONT WINDOW" displaying in the message centre for the first iteration, and it will change to "WINDOW SET" on the start of the second iteration. For the sunroof, start with it tilted, close, right back, close, tilt.

The reason for leaving the drivers door open is that if you don't, you will lock the doors and arm the alarm. The message centre will display "KEY CODE LOCKOUT" which means that the remote key will not work and you will have to wait 30 minutes before you can attempt to use the EKA sequence to open the car. The alternative is to open it with the key and wait for the alarm to stop sounding, then put the key in the ignition to reset the system.

When I did this I discovered the window regulator (the mechanics which lift and lower the glass) was worn and slipping and was not able to generate enough torque to activate the end of movement sensor (it was fine when "SET" because the electronics control the limit of movement). My local garage (Nick Kerner Engineering) said two hours labour to fit, which sounds like a good deal as it would take me all day! You may also see "SLOW: 35MPH max" or "GEARBOX FAULT" messages when starting for the first time which can be ignored.

Finally, removing the battery will reset the trip computer, and I believe, the adaptive ECU settings which will take 30-50 miles driving to re-adjust, so if it sounds "different" for any reason, give it a few miles to improve before worrying.

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A bit of PS on this subject: One other thing to note is that if the battery level is low you may observe one of two things. The first is that when you unlock the car the solenoids in the locks keep firing repeatedly without actually unlocking the doors. The second is that when cranking all the warning lights flash on and off on the dashboard, possibly with spurious fault messages ("GEARBOX FAULT" is a favourite which means that the power to the Gearbox ECU is less than 9V). In both cases the battery still has a reasonable voltage but not enough to turn the starter over.

[edit] Not Starting or Charging

I've had a report from Richard Talley that he had a problem with his P38A not starting and also poor battery charging. This turned out to be that the cable from the starter motor to the battery was badly corroded and covered in oil.

This was causing a large voltage drop to the starter motor, and also seemed to be causing a drain on charging current as well.

Worth checking if you have problems starting......

More P38A Pages

Buying - Models - Servicing - Enhancements - Powertrain - EAS Electronics - Brakes - Interior - Exterior - Security - Heating - Manual