Defender Td5 Battery Warning Light

Hi everyone, bit of a long one, but I wanted to include as much detail as I can.

I've recently been having some issues with my 03 Defender Td5, where my battery warning light has been appearing intermittently. The first time it happened, it came on for about 10 seconds, and then went out for about 10 seconds. This repeated about 4 or 5 times until I turned the car off and checked the battery connection. It then remained off for the next 6 months or so. The second time this happened in the same fashion, until I turned the car off, after which it remained off for the next 3 months. I'm not sure if this is related, but later on in that same journey my headlights wouldn't turn on, which somehow sorted itself out after turning the car off for about 20 mins. (I have now have a spare headlight switch just in case)

Yesterday I had a similar issue, but this time it was worse. The light came on and off in the same fashion as previously and I could see my headlights would become dimmer when the warning light was on, and then become brighter when the dash light was off. I then stopped and noticed that when idling, if I put my foot on the accelerator pedal, the warning light would appear, and then go off with my foot off the pedal. After turning the car off to check if the alternator had any visible signs of failure (smoke, melted wires, etc.) I carried on driving as I had to make it home. This time the warning light remained on the rest of the journey (about an hour) and occasionally would turn off for about 0.5 seconds seemingly randomly. Despite this, the car was able to carry on for this duration, even with the headlights on, albeit very dim.

Earlier today I decided I'd see if the car would start as I have heard that the Td5 needs a strong battery voltage to start, and to my surprise it started just fine and there was no battery warning light. To me this implies that the battery hadn't lost much charge, despite driving with lights on and the battery seemingly not charging.

Another thing that may be linked is when I used the Defender to jump start another car, my engine rpm dropped to idle when trying to start the dead car, despite having a friend with their foot on the accelerator to bring the rpm up to around 2000rpm.

I'm unsure on where to go from here, most of this I suppose points towards a failing alternator, but would it be this intermittent? I'm also wondering if an earth issue would cause this? Previously I have had an issue where my temperature gauge would drop to zero with my foot on the accelerator, which I solved by adding an ECU earth to the battery negative as per recommendations. Perhaps this could be linked? I have previously been over the main earth points on the vehicle and cleaned them in attempt to solve my temperature gauge issue, which made no difference.

I would like to try the cheap/free solutions first, and so I've checked fuses and I was going to try cleaning the connections on the alternator with some contact cleaner, as the alternator is rather dirty/oily. I might also go back over the earth points on the vehicle. Unfortunately I haven't got a multimeter, so I haven't checked voltages. Any suggestions of what I should try would be much appreciated.

Long winded yes, but recon you have got there in the end. Most likely a failing alternator and this could effect long term health of battery. The running issues are common with ECU control engines in that they do not like low voltages.
Modern vehicle battery lights are a pain in that they only come on when the voltage gets below a certain level unlike older ignition lights that would come on as soon as the alternator/dynamo was not charging.
Keeping earth points clean is good.
Get alternator and battery tested.
Fit a Voltmeter to your truck, this can be a simple digital read unit that plugs into your dash power socket. When engine off it will read 12v or just under with a good batt. With engine on it should read 14v or there about.

Another thing that has confused me about the TD5 charging circuits is that the feed from the alternator to the battery is different from the feed that makes the warning light come on or go off. The former is the big nut on the side and the latter is one of the wires on the multiplug. So, depending on what's wrong, the warning light stays off but the battery fails to charge, or the battery is charging as normal yet the warning light is on. As well as the earths, it's probably worth taking the multiplugs apart and giving the pins and sockets a spray with electrical cleaner and push them in and out a few times to get rid of the verdigris. Plus, water can creep in so a dose of ignition seal when they're reassembled can help too. Especially in the winter when there's salt on the roads.

My money is on the alternator also, but it wont be long before it takes out the battery too.

Col

Thanks for the replies, just thought I'd update this.

I decided to fit a new Denso alternator and so far I've done about 300 miles with no warning light or apparent charge issues, hopefully it remains this way. The old alternator was a genuine LR part, so I assume it is the original. At nearly 20 years old I suppose it's done quite well.

I had to change the alternator without removing the viscous fan (I haven't got the correct spanners) so I thought I'd share my findings, as I couldn't find much information if it was possible to do it this way.

• Obviously access is limited with the fan in place, but I was able to reach all relevant bolts with spanners and sockets - just took longer to undo some of them
• The Land Rover Workshop Manual says to remove both ends of the oil feed pipe, but I only removed the end going into the alternator. I also only removed the alternator end of the upper support bracket
• The Workshop Manual also says that the tensioner bolt is a left-hand thread - mine wasn't (not sure if that's a mistake in the manual or if it is referring to the bolt that actually holds the pulley wheel on to the tensioner assembly)
• The lower alternator bolt requires a Torx T50 bit to remove
• To actually get the alternator out, I found I had to remove the lower bracket to the engine block (3 bolts) and the propshaft. I then took the alternator out via the back of the engine (going beneath the starter motor). I found that there was a hose (EGR cooler I think) that stopped me removing the alternator out from the side of the engine
• Whilst everything was out, I cleaned up all the hoses, brackets and bolts as best I could
• To refit, I loosely fitted the lower bracket to the alternator whilst it was out of the car. I then put it back the way it came out. To actually get it in position was quite hard, as you have to hold it in place with one hand whilst getting the lower bracket bolts in. With these bolts in loosely, I could manoeuvre the alternator a bit to get the oil drain hose on. Once that was on, the rest was a reasonably straight forward refit of bolts/hoses/connectors.

Overall, not too bad of a job. I will make sure to update this thread if anything changes

I have one of these on my battery, it's not super sophisticated but it does indicate if the battery is being charged or not and the voltage coming out of the alternator over time.