Electronic Diagnostics
Tracing and fixing faults in electronic engine management systems
Land Rover’s luxurious MPV is liked for its strong off-road credentials and sheer practicality, but how do its diagnostics fare? Kim Henson and Edward Haggar investigate the Discovery 3 V6 diesel.
Providing competent performance both on- and offroad, Land Rover’s Discovery has been a hit since the first versions arrived in 1989. More affordable than the Range Rover on which it was based, the Discovery quickly earned a reputation for toughness and usefulness.
Second-generation Discoverys arrived in 1998. Versions included a 3.9-litre V8 petrol model and five-cylinder 2.5-litre Td5 diesel, with power coming from Rover-derived L-series engines. The Discovery 3 was introduced in 2004, featuring an innovative form of body/chassis construction (Integrated Body Frame), which incorporated a combination of monocoque and separate chassis elements. Also notable was the sophisticated all-independent air suspension system, enabling ride height variations to be made.
Under the bonnet was a 4.4-litre petrol-powered V8 or a torquey 2.7-litre V6 diesel unit that was jointly developed by Ford and PSA, but it’s very rarely encountered in the French company’s vehicles. A wide variety of electronic control systems was used to operate the suspension system and transmission aspects, as well as engine management. Discovery 4 models ousted the third-generation in 2009.
The subject of our feature this month is a 2005 2.7-litre V6 turbodiesel variant of the Discovery 3. It operates with a Siemens SID 201/4 management system. Edward Haggar guides us through the intricacies of this model.
When the Discovery 3 was launched, it impressed with its contemporary looks and the number of gadgets built into the vehicle. However, with these new models came many problems and recalls. Once these niggles have been overcome, they are very capable, reliable vehicles. Many owners rely on their Discoverys because of the model’s strong towing abilities, particularly over difficult ground conditions.
Preparation
The Discovery is very easy to service and a competent DIY mechanic should find the job straightforward. It is always advisable to use only high-quality components, including filters, etc.
A good, solid jack and axle stands are essential due to the considerable weight of the vehicle. Once the engine undertray has been detached, there’s plenty of access to remove the engine oil drain plug (13mm spanner size).
The oil filter is located under the engine cover, in the centre. A replaceable element is used, and a 36mm socket spanner is required to gain access. The air filter is easy to reach, positioned beneath a clip-on cover on the left-hand side.
By contrast, the fuel filter is rather more difficult to reach, being mounted under the front of the vehicle and behind the right-hand front wheel, hidden by a cover.
In theory, these engines are selfbleeding in terms of pulling air-free diesel fuel through the system on restarting following any dismantling, but in reality they can do with a bit of help. We strongly recommend pre-filling the diesel filters with either neat diesel fuel or an additive, which saves the starter motor from taking a pounding as it struggles to crank the engine for long periods while attempting to draw up fuel.
Note too, that the high-pressure fuel pump drivebelt is hidden away at the rear of the engine. The belt tensioner sits on a lug and setting the tension is not easy as it is virtually impossible to see. If the tensioner is not fitted correctly – ie, if it is fitted at an angle rather than squarely – the belt can snap.
From a diagnostic point of view, a basic code reader enables you to carry out many checks. However, for jobs such as resetting the service indicator lamp and working on the handbrake system, a more sophisticated tool is needed.
It’s worth noting that, due to the rugged nature of the vehicle, Discoverys are hard on tyres, brakes and suspension components. On the plus side, many of the tools required to work on the suspension are readily available and there are also firms offering a rental service for these.
Fault 1
HIGH-PRESSURE FUEL PUMP DRIVEBELT FAILURE
Our first fault – non-starting of the engine or cutting out and refusing to restart – relates to a maintenance aspect that is often overlooked because of its inaccessible location. The problem is the high-pressure fuel pump drivebelt located at the rear of the engine. If the belt snaps, the engine won’t run.
It is recommended that this belt is renewed at the same time as the cambelt at the front of the engine, but this often doesn’t happen as the belt is notoriously difficult to reach. It’s possible to replace the belt with the engine in situ, using an angled mirror and relying on feel. However, some mechanics prefer to lift the body from the chassis and complete a few other jobs at the same time. The good news is that there is no complex timing/alignment procedure for the belt, as it is simply adjusted via the eccentric tensioner and lining up a mark.
From a diagnostic point of view, the easiest method of checking the belt is to observe live data for high pressure and, if the belt has broken, you will see ‘0’. We have come across high-pressure pumps failing, but only very, very rarely.
Fault 2
DEFECTIVE EGR VALVES
When our second fault occurs, the vehicle will suffer from a lack of power and, depending on how badly the exhaust gas recirculation (EGR) valve has failed, it might be undriveable.
EGR valves are fitted to most modern vehicles to reduce CO2 emissions. The EGR system takes the gases from the exhaust manifold and directs them back into the cylinders at lower temperatures, which produces less harmful nitrogen oxide gas. However, this process creates more soot, which can eventually build up and prevent the valves from operating properly.
Some professional mechanics say that they have blanked off both valves with success, although we have never tried this solution. You could try using a borescope to confirm the position signal, but experience says that the symptoms are most likely to be due to an EGR valve problem.
The likely fault codes stored will be ‘P140A Exhaust gas recirculation sensor C – circuit low’, ‘P140D Exhaust gas recirculation control circuit B range/ performance’ and ‘P140E Exhaust gas recirculation position sensor C minimum/maximum stop performance’.
It’s worth cleaning the valves and pipework, although reaching the valves
is not a five-minute job. However, if the problem has reached the stage where the warning lamp is illuminated, it is likely that the valves will be too sooted up to be able to clean them anyway. Always inspect all the rubber pipework – if the pipes are split, sluggishness and black smoke will result.
Fault 3
AIR SUSPENSION SYSTEM AILMENTS
If the driver is seeing a dashboard warning indicating air suspension system faults and, at the same time, finds it impossible to alter the ride height settings, a diagnostic check should be carried out. The code ‘C1A2064 Pressure increases too slowly while filling reservoir’ may be stored.
The first thing to do is check that no part of the system is suffering from leakage, with soapy water sprayed over the suspension airbags highlighting any air leaks. In most cases, the pipework will be found to be OK. If no leak is discovered, it is likely that the fault is in the air suspension compressor. This is located on the underside of the vehicle, on the left-hand side.
The problem is that the exhaust valve sticks and doesn’t hold pressure. You may be able to strip down the assembly, clean and refit it. However, exchange compressors are readily available. Main dealer prices for such parts may seem expensive, but there are many specialists selling the required components more cheaply.
Fault 4
FAILING REAR DIFFERENTIAL
If the rear differential unit is emitting droning, whining or humming noises, most noticeable at constant speeds, it may be suffering from dry bearings within the assembly. To check this, remove the differential drain plug and drop a small amount of oil removed into a clear jug. Look for silver filings similar to glitter in the oil; if present, these indicate that the gears/bearings are wearing and the unit will need to be renewed. Replacing the differential is fairly straightforward, but the unit is very heavy, so this is definitely not a job to attempt by yourself.