ABS diagnostics

[Roger1950]

The code flashed on the LED and the dashboard alarm light simultaneously.

[Roger1950]

The dealer had removed the bulb in mine to hide the ABS fault (Pre MOT failure time) ..

Checked the brake lights .. normal bulbs .. not LEDs ..

I metered all the wheel sensors for resistance and they where all OK ..

Fed 12volts to the ABS pump .. that 'fired' up OK ..

Checking for continuity (broken wires) .. more by luck than skill .. found a poor multi pin connection by the ABS valve block .. (sorry for crappy pic)..

Mike, did you have a fault code? Like, perhaps one for the pump?

[mikeWalsall]

I do have a JDM reader .. but it would not 'latch on' / connect .. so tried the paper clip method but could not get any 'readable' codes ..

My JDM reader on my V6 Alphard works OK ..

[Bongolia]

Well that pretty much puts the dodgy PCB to the back of the queue then.
Roof light stayed on continually during this I expect?

[Roger1950]

Hi Bongolia

I took a break to go walking in The Lakes (very nice, thank you.)

Back at the ranch, I checked each item you suggested:

1. the fault presents when the ignition is switched on. The ABS warning illuminates and does not go out. From this I have been assuming that the ABS system is failing its self-test OR it is OK but there is a legacy fault code in the ECU. I have tried the ECU reset methods suggested (disconnect batteries, leave for a couple of hours) and also the ignition on/pump the brake pedal method. No change was noted.
2. The toothed rings on the front hubs look OK as do the rings inside the rear hubs.
3. All tyres are the same size.
4. No noise from wheel bearings that I can detect.
5. My "spare" sensors are second hand and I don't know for sure that they are OK.
6. I made up a sensor test lead and drove at 20mph. The two front sensors each output 3.6 volts AC. The left rear sensor outputs 1.3 volts, and the right rear outputs 0.4 volts. One of the spares outputs 1.1 volts and the other outputs 0.4 volts.
These results are pretty ambiguous - should all sensors output the same, or is the ECU programmed to receive a different voltage from the front and rear? What should the voltage be?

Roger

[Bongolia]

That is strange innit! The rears being so different from the fronts volts wise and quite a difference too.
That could be due to a number of factors like differing wheel sizes on axles, reluctor size, air gap or maybe the sensors differ between the axles etc.
When you checked the rear reluctors did you notice if the air gaps were the same on both sides?

The voltage will increase with road speed so you will not have a set voltage generated normally tops off about 5-7Vs I think. Someone on here may know.
It would be nicer if you had closer readings across the rear axle though.
Maybe for now add back the sensor to give you the most equal output on the rears.
Did you take the readings directly from the sensors as opposed to the ECU end?

When the ABS self tests among other things it checks the resistance of each of the sensors (around 1100-1500 ohms) and the cabling if that comes back wrong then it will set up the warning light and the default is usually to disable the ABS function.
Did you get a chance to slam the brakes on to see if the ABS was working? All sensors plugged in of course.

Assuming the fault codes were cleared and the self checks immediately found the fault still present so holding on the warning light and
as the fault code shows the fault to be on the front and as the voltages from the front sensors were good and close then subject to the resistance readings being OK I would guess that you have pretty much proved the sensors are good. I guess your next port of call is the wiring from the ECU plug to the sensor(s).
You would need to check the resistance/continuity of these cables from the sensor plug back to the ECU giving them a wiggle test in case there is a break in the cabling.
Geoff may have a wiring diagram showing the pin outs that would help here.
Historic faults do not normally put the light up they just sit in the background until looked for.

[Roger1950]

Bongolia, thank you for the thoughts.

The reluctors (toothed rings) are different at front and rear. At the front they take the form of a toothed disc, and the magnetic piece of the sensor is clearly visible. At the rear, the sensor is inserted into the hub through a hole. When I removed the rear right sensor, I was able to see the toothed ring within the hub. All was clean and tidy. The air gap between the teeth and the sensor is fixed by virtue of the depth of the bore that the sensor locates in.
My gut feeling at the moment is that both rear sensors are u/s and that they should be generating a similar voltage to the front ones.

As I reviewed your post, I decided to re-check the diagnostics box, along with the comments from Geoff. I studied the various posts and the photos, diagrams etc. I believe I had been using the wrong pins - the code 35 was incorrect - must be for something entirely different. When I connected the jumper and the LED correctly, I got code 03 repeated on dash and LED simultaneously. (Incidentally, this was the code that the garage reported several months ago, which they took to mean a u/s rear right sensor - don't know why - the code should be 13.)

Anyway, this all leaves me somewhat at a loss to know how to proceed. I will think about it for a couple of days - I may try a front sensor in a rear hole, just to see if the voltage is low by design. If the sensors were a sensible price, I'd replace both rear ones right away but it's a bit of a spend when you are not sure if that is the problem.

Slamming on the brakes brings us to a rapid halt but no ABS action.

I checked the sensor voltages using a test lead, rather than going through the vehicle wiring to the ECU plug. I previously checked continuity/resistance of the sensor wiring back to the ECU plug (using Geoffs wiring diagrams) - all looks good.

Thanks again for the explanation of the ECU self-test actions.

[Roger1950]

Mike

I removed the heater ducting and checked the plugs you showed me. All looked secure and all the terminals were clean after I opened them up. Re-mated them but no change.

Thanks for the info.

[Bongolia]

Mike

I removed the heater ducting and checked the plugs you showed me. All looked secure and all the terminals were clean after I opened them up. Re-mated them but no change.

Thanks for the info.

Thats OK but you may have a fault in the wiring from the ABS unit to the sensor hence the need to meter those cables.

[Roger1950]

Yes, got that. I have checked the wiring between the sensors and the ECU plug (all good.) From the wiring diagrams, the sensor wiring goes to the ECU but not to the ABS hydraulic unit (which is where the plugs mentioned by Mike were his culprit.)

[Bongolia]

Sorry,somehow missed your post before last.
Yes, if the sensor is interchangable that would be a worth a try. If it dhifts the fault to the front.
Did you check wiring from ECU to ABS module too?

[Bongolia]

So we are back with the OS rear as indicated by the fault code 03 (s/be 13)?
I am not having any luck cross refs on the ABS unit I am afraid SO9V 43 7AO doesnt show and the Nippon site may as well be in Japanese
Was the lowest voltage reading sensor on that OS rear and did we try unplugging the ABS ecu to clear the codes?
I think maybe I need a reset

[Roger1950]

Thanks Bongolia.

Next week I'll check the wiring from the ECU to the ABS unit, and try a front sensor in the rear OS.

But it is time for a break, indeed. Have a nice weekend

[Bongolia]

Thanks Bongolia.

Next week I'll check the wiring from the ECU to the ABS unit, and try a front sensor in the rear OS.

But it is time for a break, indeed. Have a nice weekend

Agreed.
Nippon ABS LTD do have a facebook page!