Couldn't think of a better section in which to post this. It's not limited to engine and involves some electrics (which has no dedicated section), but it may not be electronics related. So I posted it here.
I've had my SL (see below) for some years and starting has never normally been a problem. When not in use for any extended period I have 2 CTEKs to keep the batteries in tip top condition. But twice I have now experienced a problem trying to re-start the car.
Most recently this came after it started perfectly in the garage (CTEKs had been connected), then a 30 minute drive after dark and switched it off. Within a couple of minutes I tried to re-start the car and the tortuously slow cranking of the engine gave all the appearances of a low battery. I was just using the shift lever Start button and don't believe I tried the actual keyfob in the switch. I tried a few times, but it was turning over so slow it wouldn't start. Somewhat perplexed as I thought this had never happened before, I arranged for an emergency break-down call out to come and help. After a few more minutes, having got out and locked the car, on the off-chance I unlocked it, got back in and tried to start it again. Cranking slightly faster it eventually caught and started. Without trying to diagnose it further, I cancelled the call-out and drove home, carefully avoiding having to stop the engine and parked it in my garage (without connecting CTEKs), using a different car to continue the evening.
The next day I tried the car again and it started perfectly. Several times and showed a decent 12+v when off and 14+v when running. So no obvious problem.
I am aware that the battery is not in exactly youthful, but the car has only done 20K miles and is kept garaged. Although a failed cell can cause a battery to exhibit erratic behaviour, this seems different. In particular, after starting perfectly, a short drive rendered it incapable of cranking the engine fast enough to start. Then I just managed to get it started, the same short drive home and left for about 20 hours and all appears good again. None of which is consistent with a failing battery. So I began to think.
And remembered that this had occurred before, albeit with such minor consequences I had forgotten.
This involved a longish (100ml + drive) and stopping in a hotel car park and then a few minutes later trying to re-start the car to move it. At that time, as in the more recent episode, the engine wouldn't crank fast enough to start. I decided I was quite happy with where it was parked and that I'd worry about it the next day. And then promptly forgot all about it until having walked to the car the next morning and started it easily, without any problem, spinning the engine over 'with gusto' and immediately starting and running perfectly. I then forgot all about it again.
Until it happened again a few months later, as described above. Which puzzles me as I just don't think a failing battery would behave like that. To be so perfect at all starts, except for these 2, separated by months and in each case, having been left for a while, problem has miraculously vanished.
I believe that the big rear battery can in some circumstances charge the small front (starting) battery, which would explain how after sitting a while, it was able to start. But it does not explain why the starter battery became so low. Both times after a drive long enough for a fully functional charging system to bring it completely to full charge. But if the charging system is at fault, why only those 2 isolated incidents in the several years I've had the car.
Which makes me think the complex electronics in this car may be the culprit. Is it possible that in some circumstances, trying to re-start after only 2 or 3 minutes would somehow confuse the system into not providing full power to the starter. Is it even possible to be restricted in this way?
One other similarity in the 2 incidents, that may or may not be relevant - in each case, when trying to re-start the car, I fumbled it. Thinking about other things I pressed the start button before placing my foot on the brake pedal. Realising my mistake I pressed the brake, then thought that wasn't the best way, took my foot off, then back on and pressed the Start button (or some such similar sequence of fumbles) in quick succession. Could that have 'confused' the car's electronics in some way that resulted in its inability to fast crank the engine?
If I have to replace the (what is now ageing) front battery, then I will, but I'm loath to try and diagnose a problem simply by buying new parts until the problem goes away. So if the problem is actually related to some electronic control unit and not the battery at all, I don't want to find out after (needlessly) replacing said battery.
I have read a brief mention of something vaguely similar in another thread, but it was quite old and so better to start a new one specifically about this problem.
Anyone any clues as to what is actually going on?
I've had my SL (see below) for some years and starting has never normally been a problem. When not in use for any extended period I have 2 CTEKs to keep the batteries in tip top condition. But twice I have now experienced a problem trying to re-start the car.
Most recently this came after it started perfectly in the garage (CTEKs had been connected), then a 30 minute drive after dark and switched it off. Within a couple of minutes I tried to re-start the car and the tortuously slow cranking of the engine gave all the appearances of a low battery. I was just using the shift lever Start button and don't believe I tried the actual keyfob in the switch. I tried a few times, but it was turning over so slow it wouldn't start. Somewhat perplexed as I thought this had never happened before, I arranged for an emergency break-down call out to come and help. After a few more minutes, having got out and locked the car, on the off-chance I unlocked it, got back in and tried to start it again. Cranking slightly faster it eventually caught and started. Without trying to diagnose it further, I cancelled the call-out and drove home, carefully avoiding having to stop the engine and parked it in my garage (without connecting CTEKs), using a different car to continue the evening.
The next day I tried the car again and it started perfectly. Several times and showed a decent 12+v when off and 14+v when running. So no obvious problem.
I am aware that the battery is not in exactly youthful, but the car has only done 20K miles and is kept garaged. Although a failed cell can cause a battery to exhibit erratic behaviour, this seems different. In particular, after starting perfectly, a short drive rendered it incapable of cranking the engine fast enough to start. Then I just managed to get it started, the same short drive home and left for about 20 hours and all appears good again. None of which is consistent with a failing battery. So I began to think.
And remembered that this had occurred before, albeit with such minor consequences I had forgotten.
This involved a longish (100ml + drive) and stopping in a hotel car park and then a few minutes later trying to re-start the car to move it. At that time, as in the more recent episode, the engine wouldn't crank fast enough to start. I decided I was quite happy with where it was parked and that I'd worry about it the next day. And then promptly forgot all about it until having walked to the car the next morning and started it easily, without any problem, spinning the engine over 'with gusto' and immediately starting and running perfectly. I then forgot all about it again.
Until it happened again a few months later, as described above. Which puzzles me as I just don't think a failing battery would behave like that. To be so perfect at all starts, except for these 2, separated by months and in each case, having been left for a while, problem has miraculously vanished.
I believe that the big rear battery can in some circumstances charge the small front (starting) battery, which would explain how after sitting a while, it was able to start. But it does not explain why the starter battery became so low. Both times after a drive long enough for a fully functional charging system to bring it completely to full charge. But if the charging system is at fault, why only those 2 isolated incidents in the several years I've had the car.
Which makes me think the complex electronics in this car may be the culprit. Is it possible that in some circumstances, trying to re-start after only 2 or 3 minutes would somehow confuse the system into not providing full power to the starter. Is it even possible to be restricted in this way?
One other similarity in the 2 incidents, that may or may not be relevant - in each case, when trying to re-start the car, I fumbled it. Thinking about other things I pressed the start button before placing my foot on the brake pedal. Realising my mistake I pressed the brake, then thought that wasn't the best way, took my foot off, then back on and pressed the Start button (or some such similar sequence of fumbles) in quick succession. Could that have 'confused' the car's electronics in some way that resulted in its inability to fast crank the engine?
If I have to replace the (what is now ageing) front battery, then I will, but I'm loath to try and diagnose a problem simply by buying new parts until the problem goes away. So if the problem is actually related to some electronic control unit and not the battery at all, I don't want to find out after (needlessly) replacing said battery.
I have read a brief mention of something vaguely similar in another thread, but it was quite old and so better to start a new one specifically about this problem.
Anyone any clues as to what is actually going on?