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Need some advice on testing. Near new battery is losing volts. Did not notice it on short trips as I alway use a C-Teck and start out fully charged but on long trip car would not start and electronics when haywire once motor was stopped. At battery shop batter tested good and 14.0 v output from alternator. Only way to start car was to disconnect the battery and reboot the system. Got me home 500 km. Checked battery next morning 12.4 volts. Noticed the interior lights flickering so suspect alternator.
Going to be a big job to get the alternator completely out but I removed it and tipped it up in place. Removed cover and tested the rectifier using the diode on multi meter. With the meter connected to the Output terminal all 6 diodes tested ok at 0.505. With the meter connected to the negative plate the first 3 diodes gave 0.44 but the other 3 were 0.505. So i'm thinking there is a fault with 3 diodes? Does this sound correct?
There are 09 diodes not 6. You cannot test them in situ without disconnecting the stator coils. But if the warning light is totally out (best to check at night ) the diodes are fine. all diode faults show in the WL inc the one with WL ON with ignition OFF. Best put ammeter in series with the battery lead and when the computers have shut down you should have below 60ma.
Alternator comes out easy upwards after you have removed the air box and a bracket.
Last edited by Pistnbroke; Aug 17, 2025 at 01:21 AM.
Thanks The only bracket I can see is that holding the Hella coolant circulation pump so I would have to remove that pump means draining the coolant.. I was thinking I would have to remove the radiator fans and take it out that way. The car is a 2004 XKR. Cheers
The diode needs to be isolated from the circuit at least at one end. You need a multimeter with a diode test position . that meter will show infinity in one direction and 0.7v in the other if its ok.
Thanks The only bracket I can see is that holding the Hella coolant circulation pump so I would have to remove that pump means draining the coolant.. I was thinking I would have to remove the radiator fans and take it out that way. The car is a 2004 XKR. Cheers
Yes, the shop manual specifies removing the fans to gain forward clearance in order to remove the alternator.
I am pretty sure your alternator are OK. Use an Amp meter and check the drain from your battery when stationary. It also could be your battery that need replacement.
I thought the same thing with my 2000 XKR because my interior light flicker also, but that seems to be normal.
Rectifier testing
