Hi
I'm new to the forum.
Normally, I manage to sort all faults eventually. But, this fault has me stumped at the moment and I would like assistance from the forum please.
2001 Freelander 1.8L petrol 5 door
Fault is that the yellow hill decent light frequently but randomly appears on the dash on its own.
The fault code in the ABS is C1146 - Can
I've used a 2 channel oscilloscope to test the yellow//black and yellow/brown wires at the instruments and both pairs of wires at the ABS ECU - Can H and Can L appear to be producing mirrored images although I've not a clue what its saying ??
I've driven the car whilst monitoring the wheel speed sensors - all even.
I've replaced the ABS unit, but still to no avail.
I'm obviously missing something. But what ??
Any suggestions and data to compare would be wonderful
Thanks in advance
Will H

Will H said:

Hi
I'm new to the forum.
Normally, I manage to sort all faults eventually. But, this fault has me stumped at the moment and I would like assistance from the forum please.
2001 Freelander 1.8L petrol 5 door
Fault is that the yellow hill decent light frequently but randomly appears on the dash on its own.
The fault code in the ABS is C1146 - Can
I've used a 2 channel oscilloscope to test the yellow//black and yellow/brown wires at the instruments and both pairs of wires at the ABS ECU - Can H and Can L appear to be producing mirrored images although I've not a clue what its saying ??
I've driven the car whilst monitoring the wheel speed sensors - all even.
I've replaced the ABS unit, but still to no avail.
I'm obviously missing something. But what ??
Any suggestions and data to compare would be wonderful
Thanks in advance
Will H

Click to expand...

IIRC the Yellow light is not a fault Iight - its the notification light that you have enabled HDC.

The wire to the switch on the gear stick is notorious for breaking off - maybe its broken off and 'shorting' which makes the ECU think you've switched it on?

Hi
Thanks for the reply
But I always thought that it was the green symbol which denoted the selection of the Hill Descent Control
It always seems that as soon as the yellow hill descent light comes on so does a fault code 'C1146 Can' gets logged in the ABS ECU. This is backed up by the following info from the drivers manual.
Hill descent control (HDC) ’failure’ - AMBER The light illuminates briefly as a bulb check when the starter switch is turned to position ’II’. The light will flash if the brakes become in danger of overheating and continue flashing until the brakes have cooled sufficiently to enable HDC to operate again (see also ’HDC fade-out’). If the light illuminates at any other time, a fault in the system is indicated. If this occurs, deselect HDC and consult your Land Rover dealer.

Yes: activation of the HDC leads to the green light appearing (constant if in 1st or reverse gear, flashing standby if in any other gear). Amber refers to a fault somewhere in the system.

Mine's a 2001 1.8 as well. I had some "fun" with the three amigos - and eventually identified the problems on borrowing a friend's T4. Speed sensors will generate fault in the ABS, TC and HDC (the three amigos). My car had an additional problem: the Yaw (or "G") sensor was providing incorrect output. The calibration was way off, but even after resetting, the problem only went away temporarily. I replaced the sensor with a second hand one, calibrated it, and now all is well

Doing a quick google search on 'C1146' suggests that it refers to a speed sensor open circuit.

The intermittent nature of the problem probably explains why you've not seen the problem on live data. Plus, from experience, live data switches off above 8mph, so you can't leave the live data recording at usual road speeds. Frustrating!

Intuitively, I suspect that there is a problem with a cable or connector somewhere. The challenge, given that there is no record as to which sensor is playing up, is where to look!

Which diagnostic tool are you using?

Hi
I'm using a Dec Super Scan III
What's not helping is I only have just a short description with the fault code of C1146 'Can error'
I also googled C1146 and had it as a wheel speed sensor. But, I think that's for Rover not Land Rover ??

If it were a wheel speed sensor then I would have assumed that the ABS and TC lights would also have been on.
My live data with the Dec Super Scan III checking the wheel speed sensors is good and not restricted to mileage and I've graphed the speeds and at no time has any signal dropped out .

I've now used an Autel diagnostic to read the ABS codes - C1146 - 'Can error throttle position sensor'
At last progress with a tad more info. Now this makes sense - The hill descent would want to know the throttle position and an error here wouldn't affect the ABS.

Replaced the throttle body potentiometer - So far on a short test drive the amber hill descent light has remained out

The trouble is that OBD2 and EOBD only standardize the emissions-relevant codes. Codes generated by ABS systems and the like are not fixed in the same way. Interestingly, C1146 is generally a wheel speed sensor fault code on a number of different manufacturer's vehicles, but maybe not on Land Rover? Throttle position would be very important to the function of HDC: it'll attempt to maintain what ever forward speed you've specified by the position of your right foot above the pre-specified crawl pace.

Fingers crossed you've sorted it. Let us know if that lamp stays extinguished!

Oh bugger - I peaked too soon - It's back on.
I've no more time to spend on this today. But, I think I'm narrowing it down.
Something changed though initially after swapping the potentiometers ?? A wiring harness 'wiggle' test didn't high-light anything.
The engine ECU didn't see this as a fault and viewing live data, the potentiometer voltages and closed/open values are as expected and seen by the ECU ??
Hey Ho
Will H

Will, what values are you seeing from the accelerometer?

Make sure you have 10mm free play in the throttle cable. There needs to be this much so the pedal at rest sensor is well clear before the throttle pot starts to register movement.

Hi guys thanks for the info
Too busy today to spend any time on it. I will report back as soon as I get a moment

Had a bit more time to check out this fault code of C1146 - 'Can error throttle position sensor' only seen in the ABS ECU but puts on the amber (yellow) hill descent light.
Fortunately I had access to another fully functioning Freelander to compare against.
I checked all of the CAN wires with an oscilloscope and they all seemed to be viewing the same signal on both vehicles.

There was ample slack in the throttle cable.
I then inspected the original against the replacement throttle potentiometer (used) - I then noticed that the replacement potentiometer had had the fixing holes elongated ?? I hadn't stopped to compare with the original when I first installed it. I just rotated its orientation until the live data stated that the throttle was closed, ignorant to the fact that it wasn't intended to be rotated !!
So, I reinstalled the original, which could only be fitted in the one position.
Using a volt meter on to the middle (green) wire - ignition on / engine off - my test vehicle checked out at 0.74volts - Mine was 0.17volts
I then adjusted the throttle body butterfly flap stop screw in, until I matched the closed throttle voltage 0.74.

On starting the engine, the engine was revving way too high (1500RPM) and it had got no intentions of settling down.
I wasn't sure why the idle speed control valve wasn't slowing things down?? So, whilst still running, I removed the short curly rubber hose from the throttle body to the idle speed control valve and alternately blocked/opened the air way. Within a few seconds, the engine was down to natural idle.

A short test drive and all good so far. As I've been here before, I'll not do my little happy dance just yet.
Will

If you've screwed in the throttle stop screw, then the engine will rev at idle. The air intake system is balanced between a small pre-set throttle plate angle and the IACV adding additional air to maintain correct idle speed.

Adjusting the throttle plate adds air that the ECU can't compensate for, so the idle speed can't be controlled correctly.