Tag Archives: diagnostics derby

Golf / Jetta TDI with DPF and boost faults.

This Volkswagen Jetta came into us with its engine management light, DPF light and glow plug light illuminated. It had very little power and needed some attention.

Firstly we carried out a diagnostic code read to see what fault codes were causing the light to be on, several codes relating the Diesel Particulate Filter (DPF) being blocked or soot content to high and one relating to boost pressure lower than expected.

Next we tried to clear the codes and restart the car to find out which codes stayed live, in this case all the codes stayed.

We tried to carry out a Diesel Particulate Filter Regeneration which with this particular car has to be done whilst driving.

You have to drive the car in 4th or 5th gear at approximately 2000 rpm until the DPF light goes out, this can take up to 40 minutes depending on how blocked the DPF is.

The regeneration did not work, so back to the workshop for some more tests.

We tested the differential pressure before and after the DPF, this is done using a pressure gauge which is connected on to the pressure sensor pipes, if the pressure is to high the DPF wont allow you to carry out a regeneration and the DPF will need to be cleaned out using chemicals either on or off the car.

The DPF soot content on this Jetta was very high so we decided to remove the DPF and have it chemically cleaned.

DPF removed from car.

Whilst the DPF was off we decided to check in to why we were getting a code for low boost pressure, we checked the turbo actuator pipes for leaks which all seemed ok then we checked to see if the actuator was working using a vacuum tester, the actuator wouldn’t hold vacuum.

We removed the turbo actuator and tested it against a new one (see the video below)

Once the DPF had been cleaned out and we had replaced the faulty turbo actuator it was time to retest the the car.

We cleared the codes and took it for a road test, all the warning light extinguished and we had full power, brilliant.

After speaking to the customer we realised that the car had lost power several months ago and he didn’t have it looked at until now due to the fact of not just one warning light being on but three on the dash.

The car wouldn’t carry out a driven regeneration of the DPF (which they do regularly under normal circumstances) due to the faulty turbo actuator which then caused the DPF soot content to increase until it was full causing all the warning lights to come on.

The Moral of this story is ‘Warning lights are important‘ if you have a warning light come on on your car get it checked out before it causes any more damage.

Aarons Autos car service garage.

Your friendly car garage in Derby

Give us a call at Aarons Autos for more info.

Broken Catalytic Converter On This Vauxhall Mokka.

A Vauxhall Mokka came into the garage today with its engine management light on in need of some diagnostic work to find out the reason why.

After speaking to the customer we soon found out that we were not the first Garage to look at the Mokka.

It had gone into another garage who had replaced the ignition coil pack due to diagnostic trouble codes relating to cylinder miss fires, the coil pack cured the problem and the customer left happy.

After a couple of days the engine management light came on again so back to the Garage she went.

This time the diagnostic codes related to Oxygen sensor (lambda) faults? But rather than checking live data on the scan tool or checking the sensors with an oscilloscope they proceeded to change the sensors and clearing the fault codes to turn off the engine management light.

After another couple of days the light came on again but rather than take the car back to the same garage the customer looked on Google and found us, gave us a call and got herself booked in.

Once the car was in our workshop we plugged in our Diagnostic scanner and carried out a full code scan of the vehicle, all modules were clear of codes except for the Engine Control Module (ECM) which had codes relating to ‘Oxygen sensor faults’.

We then carried out some live data testing on the Oxygen sensors to see what was happening, straight away we could see a problem, both Oxygen sensors were reading the same, this is not good!

Both Oxygen sensors showing the same pattern.

The basics of Oxygen sensors are that they read the gases which are being produced by the engine before and after the Catalytic Converter, and if the Catalytic Converter is working correctly the first sensor should be switching and the second sensor should be pretty static (on idle), if this is happening then the gases coming out of the Cat are cleaner than the gases going in to the Cat meaning lower carbon emissions.

Basics of the Oxygen Sensor.

Once we had checked the Oxygen sensors were working properly (not giving false readings) we needed to check the Cat’s internals to see why it wasn’t working.

With the Cat removed it was obvious why we were getting the same readings on our live data, the honey comb centre of the Catalytic Converter which catches and burns off the carbon from the engine had broken up and was allowing the gasses to pass by.

The Catalytic Converter had broken inside.

A new Cat was fitted and we ran another scan, this time no codes returned and the Oxygen sensors were working as they should.

Both Oxygen Sensors now reading as they should.

The customer now has a car which is working as it should, more economical and with a lower carbon output.

Aarons Autos car service garage.

Your friendly car garage in Derby

Give us a call at Aarons Autos for more info.

Citroen DS3 Cooling Fan module / Resistor Fault.

This little Citroen DS3 came into us to have a look at due to the engine cooling fan running at full speed.

Firstly we carried out a Diagnostic Code Read on the vehicle, this didn’t help as it had no codes for anything let alone for the cooling fan fault!

Secondly through our Diagnostic Scanner we can operate certain modules on the engine to help us fault find, one of the modules is the high and low speed cooling fans.

When we operated the cooling fans only the high speed fan would work, this gave us a place to start, we removed the cooling fan control module to find that the resistor for the low speed fan had burnt out and required replacing.

When we rang the dealer they had six on the shelf! Always a good sign as common problem parts are always well stocked at dealerships.

Heater resistor / module

Once we had replaced the cooling fan control module (resistor) we carried out another module test using our Diagnostic Scanner and it worked perfectly on low speed and high speed.

After a quick road test to make sure the fans worked with the air conditioning and when the DS3 was up to temperature it was time to hand it back to a very happy customer.

Aarons Autos car service garage.

Your friendly car garage in Derby

Give us a call at Aarons Autos for more info.