49. UNEXPLAINED ENGINE MALFUNCTIONS: Why do cars suddenly shut down and/or suffer strange elctrical problems like the dashpanel lighting up or going out completely?

Lee Power of The Backroom explains

What is happening is the latest cars running CAN - VAN, CAN - BUS & CAN - CAN digital electrical systems are suffering from stray electrical energy that interferes with the control system.

On a lot of the CAN electrical controlled cars if one of the control systems goes down it takes the rest down with it.

With lots of digital signals going down the same pair of CAN - High & CAN - Low twisted pair of wires that are all around the modern car, If the signal gets interfered with it can really upset the control system & shut the lot down.

CAN digital wiring systems was first played about with by Bosch back in the 1980s.

I think Mercedes were the first car manufacturer to start using CAN digital systems in their cars. Then PSA Peugeot / Citroen followed on a few years later with 'Multiplex', and now Ford, Vauxhall, VW, FIAT, etc are going the same way.

Basically you have a thin twisted pair of wires in the car's main wiring loom. One is CAN - high and the other CAN - low.

The cars main body computer uses these to send digital signals to things like the radio, climate control, etc and to also talk to the engine ECU that's looking after the engine.

What should happen is the digital signal sent down one CAN wire should have an opposite mirror image on the other CAN wire.

What CAN was brought in for was to reduce weight and amount of wires running around the car.

If the CAN wires get interference from say an MOD radar station (allegedly), it can upset the digital system and can shut the car's electrical system down.

Electrical spikes and CAN wiring don't make a happy combination, Ask any TU petrol engine Peugeot / Citroen owner with a Sagem coil pack.

Also water getting into one of the connections for something on the CAN system can upset the electronics. Ask any Multiplexed 406 saloon owner with a boot mounted cd changer. After the rear light seal start leaking, water then gets in to the cd changer, the cd changer is on the CAN system, The dash lights up like a xmas tree and the electrics go haywire.

After receiving complaints from listeners to the Jeremy Vine programme, Radio Two drove a VW Passat past the radar station allegedly causing cars to shut down the other week. Nothing happened when they tried but they used an older Passat and NOT one equipped with a CAN digital wiring system so the test didnt help the more modern car owner at all.

Another point to remember with a vehicle equipped with a CAN system is the battery.

If the battery goes flat be very careful using a jump box or jumpleads because the incorrect use of either of these can ruin the expensive control unit, You MUST follow the instructions in the owners handbook to the letter or seek the advice from a main dealer.

The best advice with CAN systems when jump-starting or for battery disconnection / reconnection is look in the owners manual.

It only takes a couple of minutes to read the owners manual but a less then a couple of seconds to do some very expensive damage to the vehicle.

Huge thanks to 'LeePower' of The Backroom for this explanation.

BBC News Announcement 10-11-06

The Ministry of Defence has admitted that a fault at an RAF radar dome was responsible for causing electrical problems with dozens of cars.

Engines and lights cut out and speedometer dials swung up to 150mph as motorists drove past the dome.

At the time the MoD said there was no guarantee that the Trimingham radar on the north Norfolk coast was the cause.

It now says it will consider claims for compensation after an inquiry found the radar was "out of alignment".

An MoD spokeswoman said the inquiry revealed the Type 93 radar spinning inside the dome had been out of alignment between November 2005 and February 2006.

The spokeswoman said that there was no danger to the public or personnel but the MoD would now consider outstanding compensation claims on a case-by-case basis.


On Ford Focuses, instrument panel failure can be due to the failure of the speed sensor in the final drive. Costs arounf £90 to £130 to replace.