The PD (pump injector) unit is held in the cylinder head by a single side bolt. Over time the seat works itself loose: the mounting slackens, the copper ring no longer seals, and hot combustion gas blows past. First you hear a characteristic "puffing", rhythmic blowing noise from the top of the engine when cold, soot appears under the cam cover, and then the seat surface in the cylinder head erodes. At that point replacing the seal is not enough: the head has to be refurbished or replaced. It affects PD engines between 1998 and 2010, regardless of size.

The light, magnesium cased MQ200 and the MQ250, sized for higher torque, are the most widespread manual gearboxes in the transverse engine VAG models. Both have the same two weak points, and both depend on use.

The PD injectors (on the 1.4, 1.9 and 2.0 TDI alike) are driven by the camshaft itself, against more than 2,000 bar. That wears the lobes and the rockers quickly: first a knocking noise, then a rough idle, hard starting and loss of power. The cause is the wrong oil: the PD engine requires a 5W-40 lubricant to the VW 505.01 specification, with PD approval. A plain synthetic is not enough, and on an everyday 5W-30 the lobes can wear through.

The water gets into the cabin through the windscreen drain or the door seal, and collects in the foam under the carpet. The first sign is a misting windscreen and a musty smell. The rubber hoses of the cooling circuit age and leak too. Greasy mist on the windscreen is antifreeze, plain mist is water.

The G62 sensor tells the engine control unit how hot the coolant is. If it is faulty, the control unit thinks a warm engine is cold, and runs it rich: hard warm or cold starting, a rough idle, markedly increased fuel consumption, and a dash temperature gauge that jumps around or never reaches its usual reading. The part is cheap and can be replaced in half an hour: the trouble is that many people do not recognise it and replace an injector or a lambda sensor instead. If the fault persists, the rich mixture can destroy the catalytic converter too.

The wheel speed sensor fails: the ABS and ESP lights come on, and the system drops out. The central locking actuators wear out, or the wiring breaks in the door hinge. The roadworthiness test can fail because of the ABS light.

The G28 sensor drops out as it heats up. While driving the car stops, then starts again after a few minutes. When warm it starts with difficulty or not at all, while cold it starts, so the workshop often cannot reproduce it. The fault code does not always stay stored either.