Rear wheels locking

[grogee]

Just went out for a spin in the nice weather to check all is well with the Puma after having left it garaged all winter.

There was reason to brake smartly down a country lane and the rear wheels locked. Bit frightening. My car is supposed to have ABS!

There's no ABS light on.

System is standard apart from:

ST150 front calipers & discs
Braided front hoses
+20mm spacers on rear beam hence:
Escort Estate rear ABS harness

WTF? Any suggestions? I'm at a loss on this one. Just checked Ford manual and it seems non-ABS cars have a proportioning/check valve for rear brakes (fitted in master cyl) but ABS cars don't - which is what I'd expect.

 

[grogee]

OK did a bit more investigating. Fuses OK. BUT handbook says that ABS light should come on with key in position II (ie just before you turn to III to crank). But mine does not. I suspect bulb's been removed.

Can anyone confirm their car shows ABS light with key in position II please?

Since fuses are OK then I'll start checking wheel speed sensors next. Then module as last resort (do these tend to 'go' or are they pretty reliable?).

 

[Wild E. Coyote]

Do you hear selftest of ABS on first take off after starting the engine? You should hear a slight grinding noise at the very moment you reach exactly 20 kph after startup o fthe engine. If not, ABS has not passed selftest and then the ABS light should come on and stay on

 

[mad4jags]

Hi.I can indeed confirm that the ABS and Traction control lights both come on when you turn the key.If all is well they should then both go out in around 4 seconds,even if the engine isn't running.
Sounds like someone has pulled the bulbs from the dash,probably due to a failed sensor..I'd almost put money on the paired rear...
and then a cheap replacement not working,meaning the lights stay on...I've came upon this very issue myself in the past.
You really need to use genuine Ford for the rear,Ive gone down the cheaper alternative route and they usually don't work!!

 

[grogee]

Thanks guys. No self test that I've ever noticed. Bulbs have been pulled I'm sure of it.

How I've not stacked this car into a hedge (or worse) with the brakes like this I'll never know. Hard braking is basically like pulling the handbrake on.

I'll replace bulb as a first step. Does anyone know the instrument panel bulb types?

Worryingly I do remember fitting a pattern part ABS harness and sensors when I did rear beam spacers.

 

[mad4jags]

Not 100% sure without actually taking one apart,buy from memory I think they're the soldered in diode type.

 

[Wild E. Coyote]

Diagnosing a wheel speed sensor is a straightforward job. It should read resistance of cca 1100 Ohms. If there is nothing, it is dead. Also, if you can lift the car high enough, spinning the wheel should give you some AC voltage. You should be able to read cca 0,05 to 0.1 V if you can spin the wheel fast enough. The best to use oscilscope, but multimeter should detect the voltage as well.

 

[grogee]

Thanks guys. I took instrument cluster out and you're right Mad4, all the warning lights are LEDs soldered directly onto the instrument PCB. I tried testing them but I think it's 5v which I can't replicate. There was no evidence it's been tampered with.

Only replaceable bulbs are for the backlighting. 3 or 4 I think.

I will test abs sensors next. I can get the rear nice and high no probs and from memory the connector is easy to access once you're underneath. Just need my 5 yo to spin the wheels while I test!

I guess if all the sensors are behaving it has to be the modulator, no? Unless there is a wire break somewhere. Has anyone ever changed one, it looks like a bit of a pig.

 

[Wild E. Coyote]

Complete workshop manual is flooded with popups and ads, but still you can find what you might need here:
https://workshop-manuals.com/ford/puma_1998_06.1997-12.2001/mechanical_repairs/1_general_information/100_service_information/100-00_general_information/description_and_operation/about_this_manual/

 

[grogee]

Thanks. I have the WSM via knocky Ford CD ROM and an emulator. It's pretty useless IMO. There's no mention of removal of ABS module. I can see roughly what needs doing though and it's buried pretty deep. Ah well looks like tax will have to wait until start of May now - not that I have much reason to drive anywhere at the moment!

 

[grogee]

Does anyone around Midlands have access to FDS 2000 tool or similar?

 

[Wild E. Coyote]

No need. Just get a chinese OBD2 reader (I reccomend the USB type) and Forscan (https://forscan.org) and you can do all the diagnostics on your own :grin:

 

[grogee]

Thanks Coyote. USB adapter is on its way thanks to our heroic couriers...

 

[grogee]

I tested all the wheel speed sensors and they're behaving as they should. Between 1000-1100 ohms restistance, and I get a small AC voltage as the wheel is turned. Rear ones are pattern part but seem to operate exactly as the fronts do.

I ran the car in 1st gear at idle with one sensor disconnected and still didn't get an abs light! I'm certain the modulator is dead but I've ordered kit for Forscan to make sure (useful to have anyway).

Looks like master cylinder has to come off, then brake servo, then maybe some pipes. Good job I'm not in a hurry.

 

[Wild E. Coyote]

Don't make a schoolboy error and mark the pipes to know which is which later! To know which one has to go where...

 

[grogee]

Thanks. Any idiot proofing tips are gratefully received! Especially the one about marking the pipes!

 

[Wild E. Coyote]

Don't get me wrong, they are solid pipes and bent to a position so in theory a mixup is not possible, but better safe than sorry...

 

[grogee]

Ok so how do access ABS module? It's not listed on my car.

I'm getting the feeling something fundamental has been done to completely erase the existence of ABS on my car! Is this possible?

Just as another test I disconnected ABS connector from module and put ignition on. Still no ABS lamp.

I am now thinking someone has gone in and modified the 'As Built' file and removed ABS from the spec. Is that likely?

Reason I think/know it had abs from new: it's a 1.7 Lux (I think) 2001MY with heated screen, air con etc. Not to mention the ABS modulator and speed sensors fitted to the car.

THOROUGHLY CONFUSED

 

[mmc757]

post deleted

 

[grogee]

Nope, this isn't a parking brake fault. The wheels spin freely with handbrake off, that's how I tested the ABS sensors on the rear. My problem is related to there being no ABS, despite the hardware fitted to the car. Ford workshop manual says non-ABS cars have proportioning valves to prevent rear locking up. But with working ABS there's no need for this, as each wheel is modulated according to the ABS parameters. Hence my car does not have proportioning valves (which are built into the master cyl on non-ABS cars).

The other part of the story is no ABS light, no self test, nothing - it never lights up, even when you turn key to position II.

I know the ABS sensors are working properly because I tested them. I know there's an ABS modulator because I can see it! And I know it's not working because the rear wheels lock under hard braking, I can consistently repeat this.