What Is An ECU? What Does It Do? Where Is It Located?

What Is An ECU?

The electronic control unit (ECU) used in today’s cars and trucks is used to control the engine and other components’ functions. An ECU is a computer with internal pre-programmed and programmable computer chips that is not much different from a home computer or laptop. The vehicle’s engine computer ECU is used to operate the engine by using input sensors and output components to control all engine functions. ECU’s come in many different makes,shapes and sizes. Here is a list of the most popular ECU brands used in UK cars

  • EEC V1
  • FORD

What Does The ECU Do?

The ECU needs inputs from vehicle sensors like the crankshaft sensor and camshaft sensors to compute the information using a program that has been stored in the ECU on a programmable memory chip. The ECU program will use the inputted sensor information to compute the needed output like the amount of fuel injected and when to spark the coil in order to start the engine.

There are different ECUs used for different systems on the vehicle. The different ECUs used can be for the transmission, traction control or ABS, AC, body functions and lighting control, engine, air bags, or any other system a vehicle may have. Some vehicles may incorporate more than one ECU into a single unit called a powertrain control module (PCM). These units can be an advantage by having more modules in one location but may be a disadvantage by adding longer wires to reach the component it operates.

Most newer vehicles have started using a communication line between different modules on a vehicle so they can share information and redundant sensors do not have to be used. For instance, a speed sensor at a wheel detects the wheel speed and will be an input to the anti-lock brake module (ABS) ECU. Instead of sending many wires from the one sensor to other ECUs, the ABS ECU will share the information on the network communication lines to all the ECUs that use the information, like a transmission for its shifting of gears, the speedometer to show the speed of the vehicle, or the suspension system to control the suspension as needed.

The use of sharing input sensors throughout the vehicle using only two data lines between ECUs has cut the amount of wiring used in the vehicles. Sharing information between modules also means they need a common language between them so they can operate as a group. When one computer goes down or does not share information due to an error, then it may affect other modules if they need the sensor input from the failed module.

The engine ECU in most vehicles is connected to the onboard diagnostic connector and will relay all diagnostic information on this line to all the other modules or ECUs. This reduces the amount of wire needed and you do not need to go to each ECU when wanting to test them.

Where Can I Find/Locate My ECU?

Locating/Finding your ECU is really dependant on the cars make and model. This information can be found relitivley easy on the internet. We have compiled a list of all the common makes of veichle in the UK and put the locations of the cars ECU. This will get updated regulary.


On most models the ECU is located beneath the wipers behind the plastic trim. Audi R8 has 2x ECU’s located in the rear engine bay


Continental GT Under Plastic Panel at N/S/R of engine bay x 2 ECUs


Generally is located Under Bonnet behind panel at rear of fuse box In plastic box next to battery


Citroen AX, CS, SAXO, XANTIA, XSARA, ZX Under Bonnet in engine bay


Fiat COUPE DUCATTO, MAREA, MULTIPLA, PUNTO Inside car, passenger front foot well Under Bonnet in engine bay


Ford ESCORT, FOCUS FIESTA GALAXY MONDEO PROBE SIERRA, TRANSIT Under plastic side trim in drivers side front foot well Under glove box on passenger side Next to battery Inside car, above pedals Inside car, behind centre console Inside vehicle, behind glove box New Ford Diesel Models – N/S/F Wheel Arch inside plastic box


Honda CIVIC, PRELUDE Passenger front foot well under carpet or above glove compartment


Hyundai COUPE Passenger front footwall under carpet


Isuzu TROOPER Inside Vehicle on passenger side


In plastic box next to battery Inside Vehicle under driver’s seat. In plastic box next to battery In plastic box next to battery Range rover Sport are Behind battery N/S/R of engine bay


Mazda 6 and most other models are Underneath carpet in passenger side foot well. RX8 Inside plastic box O/S/F Of engine bay


Evo models are Above glove box passenger side. Shogun/L200 are Above Passenger side outer kick panel


Nissan S13 / 300zx Inside car, behind centre console Passenger front foot well under carpet Navara pre 2005 are Behind centre console Navara 2005> are O/S/R Of engine bay X-Trial  Above Glove Compartment, 350z, 370z under bonnet


Peugeot 106, 206, 306, 307, 405 & 406 205,309 Under Bonnet in engine bay or Inside car over steering column


Rover 200, 25D, 45D, 75D Under bonnet on passenger’s side


Renault 19, MEGANE, ESPACE CLIO, TRAFFIC 21 TURBO Under bonnet on drivers side Under bonnet Under bonnet near battery


On most models the ECU is located beneath the wipers behind the plastic trim.


On most models the ECU is located beneath the wipers behind the plastic trim.


Impreza models Beneath carpet passenger side foot well


Suzuki SWIFT, BALENO, VITARA Inside car above pedals or behind glove box


On most models the ECU is located beneath the wipers behind the plastic trim
T5, T4 ECU is located under the battery tray under the bonnet.


Vectra models, under plastic trim and cover in o/s/r of engine bay New Vectra Models Are located at the front of the Drivers side Wheel arch Vehicle Selector. Zafira models the ecu is located in the passenger front wheel arch towards the front bumper

What ECU Make & Model Version Do I Have?

Once you have located and removed your ECU you will most likely like to know what make and model ECU you have. On the ECU there will be a sticker with the Make and some serial numbers. Every ECU has its own format for identifying the ECU’s model. Another way is to use the 2x PDF files below and locate your cars, make, model and it will list your ECU brand and model. If you are unsure on your cars make and model use our FREE VRM tool located in the websites footer. Just enter your cars registration number.

EGR Valves. What Are They? How Do They Work? How Can A Remap HELP?

What Is An EGR (Engine Gas Recirculation)?

EGR valves help all cars run more efficiently and completely burn fuel by recirculating a portion of your exhausts emissions and running these emissions through the combustion process again. This process results in a more complete burn of fuel, which then decreases your cars noxious emissions by prohibiting the release via the exhaust of some harmful gasses.

Why Do EGR Valves Fail?

The EGR is designed to open and close (normally electronically) at certain times through the rev range, but these valves get clogged up with carbon deposits, which can make them a fail, or even get stuck altogether either open or closed.

Every engine is different but symptoms can vary from poor idling speed, knocking, loss of power, engine unresponsive, black smoke from the exhaust pipe, and the engine management light coming on. If not dealt with, this can lead to turbo damage, a very expensive part when compared to the cost of an EGR replacement. Some theories of failure range from, poor quality electronics used by some manufacturers to the extended service intervals now in place. Should you experience any of these symptoms, contact us we may have the permanent answer to these re-occurring issues.

How Do I Solve The Issue?

By remapping and deleting your EGR valve you can make your cars engine run a lot better because when the EGR valve was in operation the ECU could prepare for the valve opening and alter the fuel and spark making a delay in detonation, but if the EGR valve is not in operation then the ECU will not alter the fuel and spark meaning there is no delay leading to a smoother running engine. Deleting the EGR valve via a remap is basically coding the ECU to not open the EGR valve ever, meaning any issues caused by the EGR valve are ruled out because it will never be used. This means that you dont need to actually remove the EGR valve which would cost a lot of money. Also if you come to Layton Remaps for an EGR removal there will be a nominal price for a remap.

  • Possible fault codes: P0400 (Exhaust Gas Recirculation Flow Malfunction) may mean that one or more of the following has happened:

The EGR passage is plugged restricting the flow of exhaust gases, EGR solenoid is faulty, Faulty EGR wiring/harness or the vacuum lines are damaged or disconnected from the solenoid or valve.

  • P0401 (Insufficient EGR Flow) most likely means one or more of the following has happened:

The DPFE (differential pressure feedback EGR) sensor is faulty and needs to be replaced, there is a blockage in the EGR (tube) most likely carbon build up, The EGR valve is faulty or The EGR valve may not be opening due to a lack of vacuum.

  •  P0402 (Exhaust Gas Recirculation Flow (EGR) Excessive Detected) most likely means one or more of the following has happened:
  • The DPFE (differential pressure) sensor is faulty and needs to be replaced, there is a blockage in the EGR (most likely carbon build up), the EGR valve is faulty, The EGR valve may not be opening due to a lack of vacuum.
  • P0403 (Exhaust Gas Recirculation Circuit Malfunction) could be any of the following:

Bad EGR solenoid, Excessive resistance in control circuit (PCM controlled ground) due to an open, chafing or damage to the harness, Poor connection at the EGR solenoid harness (worn or loose pins), Water intrusion at the EGR solenoid harness, Blockage in EGR control solenoid holding solenoid open or closed causing excessive resistance, Loss of supply voltage to EGR solenoid, Bad PCM (Powertrain control module).

  • P0404 (Exhaust Gas Recirculation Circuit Range/Performance) Usually this code points to either carbon build up or a bad EGR valve. However that doesnt rule out the following:

Open or short in the 5 Volt reference circuit, Open or short in the ground circuit, Open or short in the PCM controlled voltage circuit, Bad PCM (less likely).

  • P0405 (Exhaust Gas Recirculation Sensor A Circuit Low) Potential causes include:

Short to ground in EGR signal or Reference circuits, Short to voltage in EGR ground or signal circuits, Bad EGR valve, Bad PCM wiring issues due to chafing or loose terminals.

  • P0406 (Exhaust Gas Recirculation Sensor A Circuit High) Potential causes include:

EGR sensor signal circuit shorted to B+ (battery voltage), EGR sensor signal circuit shorted to the 5 volt reference circuit to EGR, EGR sensor ground circuit open, EGR sensor signal circuit open, Bad EGR (internal failure on EGR sensor or solenoid), Debris caught in valve and holding it open or closed.

  • P0407 (Exhaust Gas Recirculation Sensor B Circuit Low) This code has basically the same causes as code P0405
  • P0408 (Exhaust Gas Recirculation Sensor B Circuit High) This code has basically the same causes as code P0406
  • P0409 (Exhaust Gas Recirculation Sensor “A” Circuit)Potential causes include:

Defective EGR sensor, Defect in the wiring harness to the sensor, EGR pintle stuck in the closed position and a build-up of carbon is preventing it from opening, Lack of vacuum to the EGR solenoid, Defective EGR solenoid, Defective EGR position sensor, Defective differential pressure feedback EGR sensor

DPF Filters, What Are They? And How Do They Work?

Most modern Diesel cars now come with a DPF, but what does this mean for you?

Exhaust emissions standards introduced by Euro 5 in 2009 mean that all new diesel cars sold since then (and some before) have been fitted with a DPF (diesel particulate filter). The DPF helps to reduce the emissions of harmful particulates such as soot by up to 80 per cent. However, the technology has been controversial, with some car owners claiming that they have been faced with hugely expensive repairs bills when the DPF goes wrong and roadside assistance regularly called out to vehicles experiencing a partial blockage of the DPF.

The efficient functioning of the DPF can be affected by your driving habits. A DPF can mean that diesel cars are not necessarily the best option for those living and mostly driving in urban environments and making lots of short, stop-start journeys.

The DPF is essentially a trapping mechanism which captures soot as it travels through the car’s exhaust system and stops it being released into the air. Like all filters the DPF needs to be cleaned on a regular basis, a process called regeneration. This is carried out by burning the soot off the filter at high temperatures, leaving a tiny residue of ash behind.

DPF (Diesel Particulate Filter) Regeneration

There are two forms of regeneration used by modern diesel cars: passive and active. In passive regeneration, the process is carried out automatically when the car is driven at higher speeds such as on motorways or faster A roads. However, as many cars rarely make this kind of journey, manufacturers have had to develop an active form of regeneration, a task designated to the car’s ECU (engine management system).

Active regeneration occurs when the ECU senses that the filter has reached a specified limit, such as 45 per cent of its capacity. The system then begins a post combustion process of fuel injection which raises the temperature of the exhaust system to force regeneration to take place.

Regeneration Interruption

However this system can also be problematic as active regeneration takes time to complete. If the car comes to a stop during the regeneration process the cycle fails. This can cause a DPF warning light to be illuminated on the car’s dashboard indicating a partial blockage of the filter. Similarly using the wrong engine oil or driving with insufficient fuel can have the same effect. More modern diesel cars may include a special additive to facilitate regeneration, so you need to keep an eye on the level of the additive tank.

Incomplete regeneration cycles can cause the deterioration of engine oil, as the unused fuel injected to start the process drains off into the sump. If you notice an increase in your oil level or receive an oil warning, DPF regeneration interruption could be the cause.

You can manually stimulate the regeneration process by driving at a minimum speed of 40mph for about ten minutes, to give the mechanism time to complete its cycle and clear the DPF warning light. Alternatively, drive with the revs at least at 2000rpm for 5-10 minutes to produce a higher running temperature.

Don’t Ignore Warning Lights

What does a DPF warning light look like? This can be found in your cars manual. Here is a picture of a DPF warning light. Some people mistake them for an EML (Engine managment light) Which on ocassions both can be illumintaed.


A failure to respond to the DPF warning light means that the filter will continue to collect soot. When it reaches about 75 per cent, other warning lights will appear on the dashboard and the car’s performance will be restricted. At this point a more complicated unblocking process will be necessary to clear the filter, which must be carried out by a mechanic. Should the filter reach a capacity of about 85 per cent, the filter will need to be removed for manual cleaning or replaced altogether, which can cost £1,000 or more.

Most DPFs should be good for 100,000 miles of motoring but, this is entirley down to driving style, short trips, long trips, and fuel.