Is it the alternator?
An owner (2012) who charged the car every few days found it struggling to start after a day or two of commuting. His multimeter gave 12.1 V at the battery with the engine off, falling to about 11.9 V on ignition, and with the engine running only about 12.1 V rising by at most 0.1 V when revved. A donor car he jumped from read 14.8 V under the same meter, so the meter was right. A new battery made no difference. A new GM alternator cured it. See Flat battery and charging system for the voltage tests.
- Check the basics first. One owner says a loose or failing belt tensioner killed the charging on his car and the battery kept dying until the tensioner and belt were replaced. See Alternator belt, tensioner and idler bracket. Check battery terminal tightness too.
- Measure at the battery, running. About 13.5 to 14.5 V is a healthy range (one owner); if it isn't, stop the engine and check the wiring.
- Continuity. One owner suggests measuring the resistance between the alternator output and the battery positive, and the same for the earth, before blaming the alternator. A fuse between alternator and battery was also mentioned as something that can blow. Nobody confirmed whether this car has one.
- The terminals are hard to reach. Several owners say you can't easily get a meter on the alternator terminals with the car running, so test at the battery. One suggested that an alternator supplies charge only if its small excitation wire has 12 V, and that a high-current feed goes to the battery.
- The warning light. If the light stays on after the engine starts, the alternator isn't charging. In the 2012 case the light was not on yet the battery wasn't charging, which owners said suggested either a bad connection between the alternator and the battery, or a drain. One thread (2006) had a car where an RAC patrolman suspected stuck alternator brushes, but another owner thought the battery was more likely at fault. Owners warned that the alternator route can be expensive.
- A refurbishment is an alternative to a new unit: one owner had his refurbished by an auto electrical firm with a new diode pack for about £50, and says unless the car has covered high mileage, don't pay big money for a new one. Another owner replaced it with a new GM one for about £120.
Removing it
One owner's steps from memory (2012), with extra tips from others. They are not a verified procedure, so use with TIS and common sense.
- Disconnect the battery.
- Jack up the car, and remove the offside rear (OSR) wheel and the arch liner.
- Remove the auxiliary belt. A car with the short belt modification is said to be easier (one owner). See Alternator belt, tensioner and idler bracket.
- Undo the bracket on the alternator that can be seen from under the arch.
- Rather than fight the long bolt that goes through the main alternator bracket, remove the bolts (he thinks three) that hold the main bracket to the block. Standing at the back of the car you can feel the bolt heads under the alternator inside the bracket. A helper holding the alternator up helps. Another owner agrees: don't try to get the long bolt out, take the bracket off the block instead. A third found the main bolt impossible to reach and extract, because it is so long it fouls something.
- Turn the alternator round and take the nuts off the cables on the back, from above.
- It then comes out from underneath. One owner pushed a large towel underneath the alternator, let it drop onto the towel, then twisted it to get the wires off and lifted it out.
Refit in reverse. The owner who changed his did the cam belt and water pump at the same time since he had access. See Turbo cam belt and Water pump replacement (the latter is for the 2.2 NA).