Diamond Dave

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Understanding what your motorhome's warning lights mean will save you a lot of worry on tour – get the knowledge from our technical expert Diamond Dave

The number of dashboard warning lights that are fitted to vehicles has increased dramatically over the years, and these can often be confusing for new owners. However, there is a simple rule of thumb that you can apply which will help you when your dashboard lights up like Blackpool in October – a simple colour code is in operation.

In dashboard warning light terms, green means ‘go’. The most common green lights tell you that your indicators, lights and cruise control are in use – these aren’t really critical to the operation of a vehicle, but are useful information all the same.

Amber lights are a warning: these could include fog lights being switched on, a fault with the ABS, bulb failure or an engine management issue (often considered to be an emissions control system fault indicator). An amber light on the dash means that there might be a fault present in whichever system is indicated. It’s not critical to driving safety, but you should troubleshoot the problem at the earliest opportunity.

Ignoring an amber warning can lead to a bigger fault, so if one pops up, check in your vehicle handbook to see what it means and get to a garage as quick as is reasonably possible.

Red warning lights, on the other hand, mean stop at the earliest safe opportunity. These come on for a number of reasons, including issues such as low oil pressure (with a risk of engine seizure), the handbrake being left on (risk of brakes jamming or overheating), or low brake fluid (risk of total loss of brakes). Hazard warning lights illuminate a red indicator on the instrument panel because they should only be used when the vehicle is stationary – contrary to what seems to be popular belief, they do not permit you to park on double yellow lines!

If a warning lamp comes on in your motorhome, first take note of the colour. Green is for information only, and means that it’s okay to continue driving. Amber means that a fault has occurred, but not a critical one, so get it checked as soon as possible. Red means stop! A fault has occurred that could be serious and/or safety related, so continuing to drive is not an option – you could cause major damage to your vehicle or, if it’s a braking- or steering-system fault, to yourself or others.

Your vehicle handbook will give a clear explanation of what each warning lamp means, so have a read of it and acquaint yourself with them.

Why motorhome sensors matter

The modern vehicle is loaded with sensors, which help control air pressure, boost pressure, crank and cam... the list is almost endless. In general, motorhomes are all the better for these sensors – until they go wrong.

We recently had a 2008 Fiat Ducato-based motorhome in for service and cambelt/water-pump replacement. The job went well, but on the subsequent road test it was instantly obvious that there was still something wrong. The ’van had no go in it and struggled to make 55mph on the local dual carriageway.

Back at the workshop, a diagnostic scan flagged up two fault codes: a crank/cam sensor correlation error and a cam sensor error. A brief panic and thoughts of a sleepless night ensued, given that we’d only just replaced the cambelt but, after a few minutes thinking it over, I came to the conclusion that the issues were unrelated.

On the Fiat/Iveco 2.3-litre engine there are four separate locking pins to use during cambelt replacement, and all had been fitted correctly; so there was no possibility that the cam timing was wrong.

One interesting thing about common-rail diesel engines is that they need both crank and cam sensor signals to run. Because ignition is caused by the spraying of finely atomised fuel into the hot air inside the cylinder, the ECU needs to know which cylinder is on its firing stroke – and this is taken care of by the cam sensor signal.

The software in the ECU is very clever: if no cam signal is present, the ECU will inject two cylinders simultaneously – one and four together, and two and three together. This is called batch firing, and is often used in petrol engines where fuel injected to the ‘wrong’ cylinder simply sits in the inlet manifold until the inlet valve opens next time. Diesels do really need to be fully sequential, however – in other words, each cylinder injects individually at precisely the right moment.

Batch firing means the engine will run, but at reduced power; it will also have to turn over on the starter for longer than normal before the ECU instigates batch mode. I’ve seen a similar running mode on a Renault diesel car: it would crank on a turn of the key, but not fire. However, if you turned it off then immediately turned it to start, it would fire up but run poorly with lots of smoke.

It would appear that the Fiat system reduces the injection quantity when batch mode is engaged, so the engine won’t smoke excessively. Thankfully a new cam sensor in the Ducato restored normal performance – and I got a restful night’s sleep.

A keen motorcaravanner, Practical Motorhome's technical expert Diamond Dave runs his own leisure vehicle workshop. Find out more at Dave Newell Leisure Vehicle Services.
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