Tech Tips Archive from Garage & MOT Magazine

March 08 - Issue 97 GMOT

• Air in a fuel line can cause numerous problems with diesel engines and is one of the hardest problems to solve. The best way to determine that air is the cause of the problem is to hook up a clear hose to the return line. If there are air bubbles coming through the return line then it is probably getting into the system on the inlet side.
   
• Before replacing a leaking turbo several checks should be made. The oil drain from the turbo should be checked for restriction, as a bad PCV valve or crankcase pressure build-up can cause an oil leak. Oil leaking on the intake side of the turbo strongly suggests presence of an air restriction.
   
• Injectors can suffer from a drop in opening pressure, usually after several thousand miles or hours in use. A drop of 200-300 psi is normal and should not have a noticeable affect on performance. If the pressure drop is more than 300 psi, the injector should be reset to manufacturers specifications in order to assure peak engine performance.

February 2008 - Issue 96 GMOT

• Rear SAM unit failure is a common problem with modern Mercedes Benz vehicles, especially 211 chassis E-Class. A sign of a defective rear SAM is indicators not working and not bringing up a warning in the instrument cluster display. These units are easily replaced but must be coded.
   
• Peugeot 106, 206, 306, 406 1.4 / 1.8(16V) and 406 1.8(16V) models from 1996 to 2002 fitted with Sagem SL96 engine management ECU have a common fault of rough idle. This is a control unit fault, and as such, may not yield a fault code.
   
• A very common fault with the Nissan Micra is the throttle body / air mass meter. Most Micra’s will suffer from problems with the air mass meter in the cars lifetime. Symptoms include poor idle, stalling, high emissions and hesitation problems.

December 2008 - Issue 93 GMOT

• Diagnosis of the engine management on Mitsubishi Pajero 1994/95 turbo diesel vehicles cannot be carried out, as the vehicle has no electronic ecu. Some chassis and body systems can still be diagnosed as normal.
   
• Programming of new tyre pressure valves on Renault Laguna models using the opus CMT system requires the TPMS programming unit to be used in conjunction. All other functions can be carried out using the CMT.
   
• If you have a Renault Clio that is running rich and is giving symptoms of an air leak (especially petrol 1.2 8-valve with metal manifold), check the intake manifold gaskets. These models are notorious for intake manifold gasket failure.

November 2007 - Issue 92 GMOT

• Rough running and incorrect lambda readings are often caused by air leaks. A leak detection machine is an ideal tool to pinpoint hidden leaks in any system.
   
• Always exercise caution when fitting after-market wheels to late-model vehicles, as wheels that are not in spec with the manufacturers specifications can cause ABS/Traction control system faults and can void warranty
   
• When replacing a fuel pump on a modern diesel vehicle, many of these pumps need to be initialized or coded to the vehicle before they will run correctly. Make sure your diagnostic equipment can carry out this function before replacing the component. The vehicle will not run unless this procedure is carried out.

October 2007 - Issue 91 GMOT

• When working on BMW or Mercedes EHC (electronic ride height control) systems, always remember to calibrate the system after mechanical repairs are completed.
   
• When replacing one or more fuel injectors on a late model Ford Mondeo, program all injectors to the ECU, not just the replaced unit(s). This can improve fuel economy and ensure smooth running.
   
• If you have a vehicle with a battery drain problem and suspect a control unit is not 'going to sleep,' connect a voltmeter in serial to the battery terminal and monitor the voltage drop. Disconnect control units one by one until the voltage drop stops to isolate the defective control unit.

September 2007 - Issue 90 GMOT

• Misfires and rough running problems can often be located and diagnosed quickly and easily using live data readings from knock control sensors and smooth running data.
   
• When replacing an ABS or stability control ECU, the steering angle sensor must be calibrated afterwards on many late vehicles, otherwise the system will not function correctly and warning lights will persist.
   
• eOBD functions can sometimes be useful to cross-check fault codes from the powertrain system or for extracting codes from unusual or rare vehicles. However, eOBD is still very limited in the amount of information it can give you. Always try OBDII diagnostics first.

September 2007 - Issue 89 GMOT

• To reset the RPA (tyre pressure warning) lamp on a new Mini Cooper or Mini Cooper S, press and hold the button and drive in a straight line for approx 1/2 a mile.
   
• Late model Bentley vehicles can be diagnosed using VAG-group diagnostic systems, but do not code these vehicles as the coding sequences are different.
   
• If an A/C system has low gas, check for leaks! As A/Cs do not consume refrigerant, topping them up is an offence because you are knowingly releasing refrigerant into the atmosphere.

August 2007 - Issue 88 GMOT

• When working on some older Mitsubishi or Mazda vehicles, you may need to power your diagnostic unit separately, as there may be no power from the connector.
   
• To avoid triggering an airbag fault or possible detonation, always disconnect the battery when working on restraint systems.
   
• ABS wheel speed sensor faults can easily be pinpointed by driving the vehicle and reading live data from the ABS control unit.

July 2007 - Issue 87 GMOT

• Always connect a power supply and do not have the car running whilst programming/coding control units with Win-Star
   
• After replacing a door module in a Mercedes-Benz, always remember to normalise the windows for the corresponding side with your diagnostic scanner.
   
• Some older Mitsubishi vehicles have a 12-pin and 16-pin diagnostic plugs, make sure you plug into both!