Motolec Auto Electrical and Diagnostics

Motolec Auto Electrical and Diagnostics Auto Electrical and Diagnostics

It's been a strange couple of weeks with several "battery drain" faults - and many that weren't.Tests showed standby cur...
24/05/2026

It's been a strange couple of weeks with several "battery drain" faults - and many that weren't.

Tests showed standby current values well under our normal guideline of 30mA, except for one which was slightly over at 41mA but realistically wouldn't have caused the reported issue.
One was actually a charging issue, the alternator had been replaced but was giving no output.
A wiring repair was evident, with a choc block connector.
This was made good, but still no output.
The customer was questioned on the order of repairs - which was done first, the alternator replacement or the wiring repair?
They weren't sure.
Ok, where is the old alternator?
It's in the car boot.
Great! Let's test it!
The alternator was bench tested and gave a good 14.4V output.
It was refitted to the car and the complete charging system verified for operation and voltage drops. All good.
A few days later, the trade customer informed us the battery was flat again.
So now it seems we're back to the original problem.
This is what can happen when you're not getting the job first hand, additional variables get introduced.

By far the best one though was a Toyota Aygo.
Those (and their Peugeot and Citroen variants are not normally a car we see for battery drain issues.
This had a massive drain of 3.8 Amps and with the relatively small battery, would drain completely in hours.
We could see the current was flowing into the alternator.
The customer informed us the alternator was under 6 months old.
We noticed the battery warning light didn't illuminate before starting the engine.
Inspecting the alternator, we found the warning light/control wire was shorting to the battery output terminal.
Why?
Because it had been cut short, possibly due to previous damage and there was about 10mm bare at the back of the crimp.
You start questioning how anyone could think that was ok.
We spliced a new section into the wire and terminated correctly, but unfortunately the damage had been done.
The warning light now worked but the alternator still drew nearly 4 Amps with the ignition off.
A replacement alternator was fitted and luckily the battery had survived the ordeal.

It's been the typically busy week at Motolec, but with quite a retro flavour.We've had...A '91 BMW 750i for multiple li...
02/05/2026

It's been the typically busy week at Motolec, but with quite a retro flavour.
We've had...
A '91 BMW 750i for multiple lighting issues (all man made faults)
Most were rectified but there's a small shopping list of 3 lamp holders required to complete the job.
A'92 Honda Prelude for a rogue brake lamp failure warning.
We've determined that the fault is in the dash, rather than the tail lamp assemblies.
A '96 Vauxhall Vectra (one owner) for an MOT emissions failure.
The lambda sensor was responding too slowly but unfortunately the catalytic converter isn't doing anything.
It looks suspiciously identical to the aftermarket unit we've had to get in to replace it, so hopefully this one lasts a few years.

We've also had a typical mix of green crusties causing faults.
One had been missed by previous techs because the wiring harness had been re-taped without insulation damage being repaired a few years earlier.
This let the crusties set in with no external signs of damage.
Using our favourite fault location device, the fault didn't catch us out!

It's been another busy week at Motolec.Normally the sort of leaks we're dealing with are current leaks, aka parasitic ba...
19/04/2026

It's been another busy week at Motolec.
Normally the sort of leaks we're dealing with are current leaks, aka parasitic battery drains.
But this week we've had a few others to sort!

Coolant leak on an Astra from the heater matrix connections - such a tiny leak but the few drops that did leak ended up in the Body Control Module, causing random activation of horn, hazards and screen wash pump.
Replacement fittings were obtained but unfortunately the BCM did not survive and replacement work is in progress.

A Suzuki S-Cross with an air flow A/B correlation fault.
What's that?
It means the air quantity measured at point A (mass air flow and temperature sensor) doesn't equal the air quantity measured at point B (manifold absolute pressure and temperature sensor) given the physical capacity of the engine.
And why would it differ?
Well, you *could* have a faulty sensor, but the first step is to check for leaks.
We used the smoke machine to help here because some are obvious and others are not.
This one was well hidden behind the bumper!
Unfortunately the mass air flow sensor had been replaced 3 times prior to coming to us.
Hopefully the cheap one fitted actually works, otherwise it will have to be an expensive genuine sensor to complete the repair.

A Focus with a severe coolant leak filling up the driver's footwell.
This was a similar fault to the Astra, but luckily no electronics were in the firing line.
The parts required are not shown in the Ford catalogue for this model but luckily the Ford parts tech knew exactly what was needed, these were in local stock for quick delivery.

A Skoda Kodiaq with the passenger footwell filling up with rainwater.
There was already a panoramic roof fault so blocked sunroof drains were suspected.
It turned out that the module had been damaged by condensation dripping into it, but the water in the footwell was coming from the sunroof drain in an unexpected place.
Somehow the pipe seems to have shrunk in length so it won't reach its drain grommet, meaning the water was dripping out behind the dash.

What the ????How many issues can you spot here?
25/03/2026

What the ????
How many issues can you spot here?

The hottest day of the year so far, so what were we diagnosing?A Kia that won't start when it's freezing 😂With a bit of ...
18/03/2026

The hottest day of the year so far, so what were we diagnosing?
A Kia that won't start when it's freezing 😂

With a bit of simulation, we saw the glow plugs were being controlled but there was a very low current to them, 170mA.

Changing tactics we then proceeded to focus on the output side and located the massive voltage drop.

Unfortunately this was another of those instances where someone didn't pay attention in high school science lessons.

A copper wire crimped onto an aluminium busbar is pretty much a guaranteed failure.

Let's see if the replacement part is the same design or different.....

We had an interesting fault on a BMW this week, the info screen reported a central electrics failure so the owner feared...
15/03/2026

We had an interesting fault on a BMW this week, the info screen reported a central electrics failure so the owner feared the worst.
As a number of communication faults were logged, a good place to start was looking at the body network, the Karosserie-CAN.
We could see an anomaly, a group of data packets were missing half of their signals.
But which module (or group of modules) out of the 17 fitted to this vehicle on that network did those faulty data packets belong to?
None of the modules were easy to access.
A logical process led us to the faulty part of the network, but the biggest surprise was that this was an internal fault in a module, rather than an open circuit caused by a damaged wire between a splice and that particular module.

07/03/2026

Even initially simple faults can soon uncover underlying issues.
Like a Suzuki with the radio and lighter socket not working.
The fuse had blown. Just replace the fuse and send it, right?
Wrong.
This is where the forensics kick in.
Yes the fuse had blown, but it's quite easy to determine if the fuse blew from a short or an overload.
In this case, it had blown from an overload.
Was the radio faulty or had something been plugged in to overload it?
The radio seemed to work, but only on the mid/tweeters in the dash.
Not the door speakers.
Why? Because the car wasn't built with them!
We spoke to the customer for more information.
Yes, a fan heater had been plugged in to help clear the windscreen!
Why? Because the car's blower doesn't do a good job.
Ok, we're getting somewhere now.
Yes, the blower works on all speeds, the temperature and direction controls work but it's just feeble and a bit noisy.
Pollen filter blocked?
No, it doesn't have one.
The cause?
A few dried leaves on the inside of the fan drum!
The heater unit was cleaned out and the customer advised to keep the air intake clear of leaves.

07/03/2026

It's been a crazy busy week this week!
We've had all manner of unusual faults to deal with.
So busy we haven't really had time to take photos, but here's a selection of corkers....
A small van that would stall if you switched the headlights or wipers on 😮
Sliding doors that won't lock because someone had been messing and fitted parts upside down 😂
A BMW where the rear indicators would flash 3 times then fail, but work ok on hazards...due to CAN bus corruption by a dodgy Chinese screen 😮
A Transit that wouldn't start, it had a reference voltage fault which turned out to be a shorted sensor in the adblue tank😮
A funeral limo with a battery drain, ESP fault and charging fault...

And "faults" that aren't.
An Audi with defective rear lighting - the light strip that goes across the tailgate.
There were no warning messages on the dash, no fault codes logged.
Why?
Because that particular vehicle didn't have that build option!

24/02/2026

We're having telephone issues at the moment (aren't IP "landlines" great 😂)
Incoming calls appear to work from some networks but not others.
Please either message via FB messenger or email if you can't get through.
Obviously I'm not just sat staring at my phone, so it could be a few hours or evening before I can reply.

Thanks,
Simon.

This car had failed its MOT for no main or dipped beam headlight either side.This isn't a fault that happens instantly, ...
20/02/2026

This car had failed its MOT for no main or dipped beam headlight either side.
This isn't a fault that happens instantly, it's one that develops over time.
Once it starts, the process accelerates rapidly until the connection fails completely.
Headlamp bulb terminals run pretty hot to start with, but the problem usually starts after the first bulb change.
The action of unplugging the connector sometimes causes the terminals to be spread slightly.
This reduces the contact pressure between the two parts.
Reduced contact pressure increases electrical resistance.
Increased resistance results in increased heating of the terminals.
This softens the metal and further reduces contact pressure
And the whole process repeats....

If there are any signs of overheating on the bulb that is removed, the replacement will quickly be damaged because the connector is damaged.
To avoid this, both bulb and connector must then be replaced at the same time.
That's what we did here.
We keep headlamp connectors for H4 and H7 in stock, along with high quality Osram bulbs.

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Rear Of 29 Chesham Road
Bury
BL96LY

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