Clio 4 RS monitoring system voltage

Yesterday on a hot Canberra day (~35 degrees C) my 2014 Clio RS 200 chucked a "Check auto gearbox" error.

It locked in a gear and I was stuck until I turned it off at the traffic lights and restarted it.

I have a little OBD2 HUD and I noticed that the voltages were odd. So today I also put in a cigarette lighter voltage monitor. I thought that perhaps the digitial voltage recorded from the ECU might not be the system voltage. In fact there is a constant 0.2 V offset between them, probably just A to D variation.

My voltages vary from about 11.8 to 15.1. Typically on a cold start they sit from about 13.8 V to 14.2 V and I'm happy. But then they start to jump all over the place. The battery seems to put out about 12.7 V but often I see 12 V or less when driving down the road. The same happens often at idle: the voltage drops steadily from maybe 13.5 V down to 12.1 V.

Such a wide range seems a bit crazy. Especially I don't want to be discharging the battery when idling in traffic! Or when driving down the road. I had a VW bus with a dead alternator and it didn't end well

And I'm pretty sure that in the colder weather the HUD showed 13.8 V to 14.1 V most of the time.

I've noticed that people often fix the "check auto gearbox" error with a new battery. But perhaps the culprit is really poor voltage control and the new battery just holds out better.

GtirHil said:

I've noticed that people often fix the "check auto gearbox" error with a new battery. But perhaps the culprit is really poor voltage control and the new battery just holds out better.

Click to expand...

This seems to be the common first fix before you venture into changing the TCM.

Yup, a TCM replacement may well be in the future. I was just hoping that people would comment on whether this sort of voltage variation is normal.

Have a gander here see if it’s of any use to you.

Thanks Matt.

Yup, he does have a large voltage range like mine.

But like so many threads it doesn't actually have a conclusion. Did it work? He doesn't prove that his problem isn't based on the poor voltage control. Frankly lead acid accumulators are designed to be kept fully charged. They don't much like being cycled. So seeing my car running down the battery while driving appears to me to be crazy. My Mitsi Delica, for example, runs at a steady 13.8 to 14 volts and the batteries last forever. Likewise my old MR2 runs at a pretty constant voltage.
Is the reduced voltage just an effort to get a better gas mileage? Ignoring the damage from ruining batteries more frequently because that wouldn't show up in the eco testing?

Everybody seems to stress that complex modern car electrics need a steady electrical supply, whereas this range would make an Arduino look for a new home ;-)

I should try some other diagnostic software. My OBD2 reader states that there are no faults! Strangely like a Renault dealer

Here is another thread about edc issues.


Mick on there might be the guy to speak to about voltage irregularities 👍

There's never a positive answer, is there? ;-)

His 14.5 V constant seems a little high for me, but at least it's apparently constant. Easier for a power supply to step down rather than up. My battery is pretty new so my standing voltage is a bit higher.

I'm quite prepared to believe that the TCM fails when hot. It's not in a kind environment. A friend of mine with a similar Citroen unit just cleaned all the dust out of his and it started working fine.

There was a guy (I think from South Africa) on the Oz site who got a reconditioned RS TCM from China for much less money and it apparently worked well. I may be going that way.

Thanks for your input!

Renault certainly didn’t get the voltage management correct with the rs200
I reported it back in 2013 when I got one of the first cars
I noticed that the smart system cuts out the alternator when accelerating and cruising along and only charges when lifting off it the car thinks it needs voltage
I’ve seen as low as 11.2 and the car started ok but the wipers run slow
Lights go dull etc etc and then when lifting off the voltage goes up and all works ok for a few minutes
The car was in and out the garage with this problem and also loads of others
I was told The voltage problem was just the parameters of the smart charging system and as long as it started it was not a problem
Slow wipers and dull lights inn Renaults eyes are were not a problem as long as the car started

To ge honest I would rather have a decent 12.8 to 13.4 volts and loose a few mpg or 0.00005 of a hp on acceleration
Than have dull lights and slow wipers and
a engine gearbox emu that can’t function at low voltage