Engine Light issue & overcharging alternator

[hdtdamo5 Member Find all posts View Profile Close hdtdamo5]

I did a search, and didn't come up with much. I've got an intermittent issue with my Prado. Its a 120 Series V6 auto.

I was driving along, and the battery warning light came on, then a few minutes later (I couldn't pull over, but the car was running fine) the Check Engine Light, the ABS light and the Handbrake light came on, and my speedo dropped out.

I pulled over, turned car off, and turned it back on, and its fine. After a few minutes it does it again. I drive the 5 or so minutes back home, test the battery / charge rate with a multimeter, and the charge rate seems to be up around the 16.5-17 volts mark.

So i finally get around to installing the ScanGauge i bought last week, and scan for errors. a P0500 came up, and I did a search on here and found its "Vehicle speed sensor “A” (open/short/failure) " Ok, so what the hell is that?

I've been driving the car, and no issues, until last night, the voltage on the SG went up to around the 16.5-17 volt mark, and the battery light came on. (It seems as soon as it hits 17volts, the battery light comes on). CEL is also on. Again, a P0500 code comes up.

So, any ideas? The speed sensor would account for the speedo dropping out, but the voltage spike? Any ideas?

Anyone had anything like this before?

Cheers, Damo

[mjrandom Out of control poster! Find all posts View Profile Close mjrandom]

Despite the error code I would probably be looking at the battery or alternator as first ports of call. Get them load tested. Either of these can throw spurious codes due to voltage inconsistencies.

[Guest Close Guest]

Might need a new regulator to keep the voltages in check.

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

Damo,

First off, I would be investigation the cause of the high charging voltage as it should not be getting that high.

Do you have a booster diode fitted, if so try removing it and replacing with a standard fuse, though it is not what I would expect to see if the booster should fail, normally you would just get a charge fail or no boosting function.

IF no booster is fitted I would still replace the ALT-S fuse with another and see what happens.

If that doesn't work then try removing and replacing the plug on the alternator, if still no go then the most likely culprit will be the alternator voltage regulator.

Cheers
Leigh

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Hi Damo and one of the most common causes of high voltages like that is a loose or detached earth to the alternator.

Try checking the engine to chassis earth strap and any other main cable mounting connections.

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

I'm with Leigh, way to higher voltage. Will eventually cook the battery. You would be surprised what the alternator can trigger in way of other codes/faults. When my old 2.8D hilux alternator was on its way out it flicked up the diesel water filter trap, warning for brakes, alt light, and one other I cant think of. All due to dodgy regulator (part of the alternator). My father in laws commodore had a dodgy ABS module but was throwing up ECU light, trac light, temp warning light all and a couple of others due to a single component of the ABS module. I wouldn't be too concerned from the speedo dropping out till you fix the voltage issue. You will probably this to be throwing the code for the speed sensor. Was the speedo fine prior to the voltage issues ??......Cheers Steve

[drivesafe Senior Member Find all posts View Profile Close drivesafe]

Hi Steve M, your alternator must have been jumping all over the place, including causing low voltages, because it’s low voltages that cause those sort of sensor errors.

High voltages do not effect sensor feedback.

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

High voltage may cause sensor issues if the ECU over voltage protection kicks in.

[Steve M Addicted PP Member Find all posts View Profile Close Steve M]

Yeah Drivesafe, mate have no idea wether if it was high/low whatever, I know it cost me about $300 to $400 to fix at the time. If I remember correctly was some thing to do with the regulator at the time......Cheers Steve