Odd fault developed yesterday. Welcome ideas! ABS, Alternator, Short?

[JackDaniels73]

So fired up the car yesterday and out of the blue the ABS light is now on. More oddly though when I start the car the ABS light pulses. Turning on the headlights and they pulses too interior and exterior. Wonder if the ABS is not at fault and its something else causing it.

Plan to go through the ABS faults check tonight, but would not have expect an ABS issue to cause what I see now?

Posted a short video of whats going on: http://youtu.be/u9HCPky_NCI

Thanks for any ideas!

[shinny]

Wow, that's odd!

First port of call is to ask the ABS why the light is on: http://shinny.co.uk/toyota/MR2_SW_1993_ ... agnosi.pdf

Just thinking out loud but I wonder if the engine struggling could be the cause of the pulsing, as the alternator can only generate the expected 13V+ output when the engine is about 1200rpm (ish)... if your engine is dropping up and down to say 600ish that might be causing the visible pulse? I don't think I'd immediately jump to a "bad alternator" conclusion because if there was damage to the regulator so it created pulses, those pulses would have a much higher frequency (and probably be invisible) due to the speed the alternator would be turning.

[JackDaniels73]

So followed the ABS check procedure and now even more confused

So ignition on and all expected lights on, unplugged service plug and terminated E1 and Tc. Oddly no ABS light at all, but instead the P/S light flashes on and off at 0.5sec intervals. Not what I was expecting.

Still no wiser!

[Gullzter]

Having worked with electrical things in the past that pulsing looks like something on the car is trying to pull more volts through, the pulsing seems to be a similar speed or pulse of idle. No idea what it could be but hope that may help!

[shinny]

The error code reading sections all seem to be full of typos when they refer to Te rather than Tc, but it's worth noting both the ABS and the PAS instructions specify Tc and E1 (when they're not mistakenly saying Te) and the wiring diagrams show that they're both connected to that pin. I don't have PAS so I can't confirm if both flash at the same time on my car.

Having worked with electrical things in the past ... the car is trying to pull more volts through

Errrr... ok...

Voltage is not pulled and is generally constant (engine speed / alternator interactions aside) until the supply cannot meet the power being consumed by it. Perhaps you're referring to current being drawn from the supply (alternator and battery) and this being unable to fulfil the demand, hence the voltage dropping.

However it's interesting that the pulse starts a couple of seconds after the engine is started and, more importantly, is a brighter pulse rather than the constant light. This suggests that the pulse is surging over 12V and possibly over the expected 14.5V alternator output. If you have a multimeter handy, it might be worth seeing how the voltage is pulsing... is it going up or down from 14V?

I wonder (and again I'm thinking out loud a little) if that's actually an over-voltage pulse then it could have popped something within the ABS ECU. It could also have popped other ECUs, but that's a concern for later. If the voltage is going too high then the engine ECU could well be struggling to read various engine sensors and thus running the engine poorly.

[JackDaniels73]

Good point about it being a delayed reaction after engine start and does appear to be in tune with idle after a few seconds.

Car rev's up no issue just out of interest, but did not want to be running it up for to long given not sure whats going on.

Have a multimeter, where do you suggest to take reading from? Appologies my track record with electrics sucks

[shinny]

If you rev the car up to about 2000-3000rpm, does the pulsing go away?

If there's a voltage issue on the car you could read the voltage from almost anywhere and observe it... across the battery, in the cigarette lighter or (maybe the easiest) between the chassis and the live screw terminal in the engine bay fuse box.

[JackDaniels73]

will double check and also get some readings. Away now till Sunday unfortunately. Thanks for the help so far

[JackDaniels73]

So went to test and multimeter not working, so ordered replacement.

Meanwhile, ran a test by letting engine warm up. Interestingly after minutes of running the pulsing calms right down. Also when you are at high revs. Does pulse a more between idle and 3k revs.

Engine itself seems to rev and idle just fine.

Will report back once replacement multi meter arrives.

Suspecting that ABS light and pulsing not directly linked, but let's see!

[JackDaniels73]

Still awaiting my new multimeter, but could not resist a bit of a look around again tonight to make sure I have not missed anything.

Interestingly I noticed that my reverse lights were not working, so looked up possible reasons given testing of bulbs and wiring proved all ok. Only remaining item is the reverse switch on the gearbox.

Turns out the reverse switch in the gearbox, the alternator and the ABS ECU are all powered via the ECU-IG fuse in the engine bay. Checked that fuse and it had blown!

Now this is not to suggest its sorted, but might go some way to explain the symptoms I have seen.

Going to grab a replacement fuse tomorrow. Hopefully its just the fuse and not a fault that causes the fuse to blow. Hopefully I'll be able to test the voltages as well soon.

[JackDaniels73]

Solved. 29p and a 7.5amp fuse. v.frustrating, but pleased thats all it appears to be. time will tell.