Yawn Yawn - More HDC stuff

The other day my Freelander (2000 L series 5 door manual) HDC amber warning light came on while driving up the steep spiral car park entrance for the Grande Parade in Cambridge.

'That's odd' I thought, and duly ignored it until the day after when I took it out again, and the amber light came on as the usual part of the check sequence, and then went off as usual. However, it came on later on that journey and has been on for every journey since.

A few days later I was underneath doing something, and noticed that the first gear sensor switch was broken. Looking at Hippos '3 Amigos' warning tables from RAVE, looked like the HDC system was getting 'implausible gear position' because of the broken switch.

Ordered and fitted a replacement expecting this to solve the problem, but alas, I still have the amber HDC light on.

Since then, after extensive research on this and other forums, still no solution.

The car has the early 2 pin brake light switch, and although no problems with the brake lights, I have stripped it, cleaned it, and put it back together (still works as well!!).

Will have the shift switch apart tomorrow to check, and will recheck the first gear switch to make sure it has continuity in the right place and vice versa etc.

Other than doing the shift switch, brake light switch, and first gear sensor switch, any ideas what else?

For completeness, my thoughts are:
- Its not ABS sensors as the Traction control and ABS lights behave themselves, and ABS works fine with a hefty stomp on the brake pedal
- System is meant to clear itself when ignition is switched on if no faults, so doesn't need clearing by Land Rover dealer, more likely there is a fault
- one post mentions a second switch on the brake pedal. Couldn't see one, but any ideas on this?

Finally, can the warning light be removed from the dash? HDC will likely never be used on this car in anger, so if it looks like I have to spend many hours or much money resolving, it will just get ignored - would be nice to turn the light out as well!!!

Further to the above, been studying the RAVE wiring diagrams for Freelander 1 early ABS system this evening (TV was rubbish, wife asleep etc).

The ABS and inputs from HDC are all pretty straight forward and should give a clear idea on what to test (assuming the ABS ECU is not at fault).

-Diesel Engine control provides throttle position info, so as long as the diesel throttle pot on the pedal is working, should bot be an issue if the signal is arriving
- ABS ECU checks the 1st gear position. Not sure how it detects an implausible gear position from that, but will research. Looks like it just sends a signal to earth if the sensor has continuity
- There is a diag socket out and an ignition power in
- The HDC switch on the shift. Looks like this is just a simple voltage that the ECU detects if the switch is on. The ECU does the logic to check what gear etc
- Reverse gear sensor. Circuit looks like a voltage signal to the ECU which makes sense as the gearbox switch also switches the reversing lamp
- A speed sensor
Outputs to the instrument cluster for the warning lights and HDC info light (the green one)
- Outputs to the ABS modulator solenoid valves

All pretty straight forward and expected, so without a fault code to tell what is going wrong, looks like there are 5 HDC inputs to check to make sure a signal is arriving as expected.

Just need some info to say what those signals are meant to be and should be easy to work through.

Has anyone delved into this and the ABS ECU logic (relative to HDC of course) other than the posts indicating what normally to replace?

im having lots of problems finding out my TC/HDC light on i have ordered a new ecu as the wires i have checked are working to my knowledge

the 1st gear from what i remember was a earth signal and when in 1st gear it cuts the earth out so least thats what mine did

The yellow ( ! ) light is often caused by the throttle pedal switch which is independent of the EDC pedal position sensor.

Nodge68 said:

The yellow ( ! ) light is often caused by the throttle pedal switch which is independent of the EDC pedal position sensor.

Click to expand...

Thats interesting. Do you know where the throttle pedal switch is located?

Looking at the RAVE manual for the 2000 L series, the wiring diagrams and diagnostic info don't mention a throttle pedal switch. Socket 504 pin 10 carries engine ECU related information including throttle position, which on the diesel, the engine ECU gets from the fly by wire system. Throttle would not work if the engine ECU is not picking up a valid signal from the throttle potentiometer, but I guess there is a chance of corrupt data between the engine ECU and the ABS (although ABS and traction control would be impacted).

Have just been through every HDC related input on the ABS ECU (old type, under the drivers seat), and taken multimeter measurements based on the RAVE info. All inputs are functioning as specified. Retested the 1st gear select and HDC switch and all good.

Next step is to get the fault codes read and cleared and see what this shows.

Would appreciate some guidance on the throttle position switch as RAVE seems to indicate such a thing does not exist on a 2000 L series

Ah ha - More exciting HDC stuff.

Excerp from RAVE Freelander Workshop manual, Brakes section, description and operation, diagnostics

A shuttle valve switch fault, sticking throttle and implausible gear input are classified as permanent faults. If a permanent fault is detected, the related warning lamp illumination and default strategies are automatically employed in subsequent ignition
cycles, even if the fault is intermittent, until the fault has been rectified and cleared from memory.

So this suggests that if I have had an implausible gear input due to the first gear selection sensor, the fault will remain in ABS ECU memory for every subsequent ignition cycle until the fault is cleared by a diagnostic tool.

Implausible gear input is quite feasible based on the way the gearbox switch is constructed, so bear with me if interested, or stop reading if not

To detect first gear selected, the ABS ECU needs to know that there is a direct circuit to earth when in first gear. Inside the switch, there is a plunger, a small metal disc, 2 contacts (signal in and signal out), and a small spring. When not in first gear, the spring holds the metal disc away from the contacts. When in first gear, the selector rod in the box pushes the plunger in, acting against the spring, and forcing the metal disc to make contact with the 2 contacts, allowing a signal from the ECU to earth.

When my switch broke (long story involving axle stands, no front wheels or undertray, and rain sodden hard standing) the plastic end holding the contacts and spring fractured allowing the spring to dislodge. It is quite feasible that the disc was resting against the contacts when other gears were being selected.

Not sure how the ECU determines an implausible gear input (maybe road speed when detecting first gear?) but pretty certain it would not like thinking its in reverse and first gear at the same time!!

So this leads to some interesting thoughts (interesting for some!):

- On the 2000 L series (and possibly pre-2000), the brake light switch seems to have nothing to do with HDC (although note that the ABS ECU does activate a relay which operates the brake lights when HDC is active
- On the same car, there seems to be no throttle/accelerator position switch. There is a fly by wire system that gives throttle position data to the engine ECU which in turn returns data to the ABS ECU
- Some ABS fault codes do need to be cleared from the ABS ECU to make them go away after the fault is fixed

With RAVE being freely available and fairly easy to download and get set up on a PC or CD, the best way forward seems to be to navigate RAVEs fairly complex chapter structure, which when deciphered gives some very clear descriptions and diagnostic information. With this info it took about an hour to check inputs, which at worst might save a code reading expense.

The pedal switch is mounted on the pedal bracket close to the pedal pivot. As far as I know all models have them.

Nodge68 said:

The pedal switch is mounted on the pedal bracket close to the pedal pivot. As far as I know all models have them.

Click to expand...

Only thing mounted on the pedal bracket of mine is the fly by wire potentiometer.

Will take a photo tomorrow if I can work out how to include photos in the thread.

As mentioned, per RAVE, there is no mention of a pedal switch providing input to the ABS ECU. The only throttle related data comes via the engine ECU.

Below is the pin out for the main HDC plug into the ABS ECU. There is also a plug C505 which is the ABS sensors, and plug C506 which is the ouputs for the ABS solenoids, plus the ABS brake light relay.

Pin 10 and the note relating to it is the one of interest, and relating this to the wiring diagram in RAVE for ABS, pin 10 takes its info direct from the engine ECU.

Might be different on later models, as the brakelight switch certainly is and a post somewhere mentioned an accelerometer connected as well, but the pins below are a good match between RAVE and my L series, and its pretty easy to see the accelerator bracket assembly and what is attached to it.

ABS ECU connector pin-out details
Connector C504
1. Battery power
2. Ignition power
3. Road speed
4. Not used
5. ISO 9141 K line
6. Not used
7. Reverse gear selected
8. Return pump monitor
9. Not used
10. ECM input
11. First gear selected
12. Earth
13. ETC warning lamp
14. HDC selected
15. Not used
16. HDC fault warning lamp
17. HDC information warning lamp
18. ABS warning lamp

NOTE: ECM input (C504/10) contains data on throttle position, engine torque, engine speed and
engine type.

Just to top this off for those interested:

Have not posted a photo yet (being dim on how to post one) but after a good look into the darkest recesses under the dash, I can confirm that the only electrical item hanging off the throttle pedal bracket of my L series is the fly by wire pot. Are there any other L series owners out there who could confirm?

Got the car on to a diagnostic tool today, and no codes showing for anything, but HDC warning light on. THis was reset, and has not come back on again, and the HDC green light is on and performing as it should.

Conclusions

- On the L series at least, brake light switch plays no role in the HDC part of ABS system, and nothing on the throttle pedal to link in either. ABS system does control the brake lights via a relay and does a check on the relay resistance at start up. ECU sends throttle position data to the ABS system.

- There are a number of faults mentioned in RAVE that will turn on the HDC amber warning light. These are all easy things to check on the car with an ammeter, and using the RAVE ABS ECU pin out diagram, very easy to work out what might be going on.

- There are 3 faults mentioned in RAVE that will keep the amber HDC warning light on (i.e. faults not cleared at start up). These will require a diag tool to clear them

Hope thats useful and has dispelled a few urban myths for the L series HDC set-up