ABS and TCS warning lights

[PeterW]

I have the following symptoms and wonder if anybody can help with what might be causing them:

ABS warning light stays on after engine starts and TCS warning light goes off. TCS warning light comes on after driving away.

My NSX is model year 1995 MT but has the later ABS upgrade - not sure if it's '97-'99 or '00-'05.

When I short the blue SCS under the passenger glove compartment with a paper clip, the ABS light stays continuously on and the TCS light flashes code #42.
When I short the two pin connector which is next to the ABS unit under the bonnet (which was installed with the upgrade), the TCS light stays on continuously and the ABS light flashes #15, #61 and #13.

The 1995 FSM page 19-86 indicates TCS DTC #42 to be the LF wheel sensor.
I'm assuming I should use the 1999-2005 FSM for the SCS which is under the bonnet. Page 19-49 doesn't say anything about DTC #15 or #13 and says #61 is the transmission control module.

Anybody ideas what my problem is?

Thanks

[Kaz-kzukNA1]

With the upgraded ABS, please refer to the 00+ workshop manual but only for the ABS section.
Note that with the 00+ ABS, you can't erase the ABS error code without using the combination of three items – the IG key/brake pedal/SCS terminal.

Therefore, removing the fuse or disconnecting the battery won't erase it, unlike the 91 - 99 Classic ABS.

TCS #4-2 is for the FL (Front Left) w/speed sensor.

ABS #13 is for the FL (Front Left) w/speed sensor open/short circuit.
ABS #15 is for the RR (Rear Right) w/speed sensor open/short circuit.
ABS #61 is for the FSR (Fail Safe Relay) +B voltage too low.

The raw w/speed sensor signal is handled by the ABS brain first.
Then, the signal is filtered and level converted before being transferred to the TCS.

Therefore, any w/speed sensor failure would first trigger the ABS light followed by the TCS one.

Since you only have the FL sensor failure on the TCS, most likely the ABS #15 was triggered in the past and not on this occasion.

Did you see the ABS light and/or replaced the RR w/speed sensor in the past?
Also, it can be triggered if IGSW P2 On AND the w/speed sensor connector disconnected.
Again, you can't erase the error code from the ABS brain without using the above method.

ABS #61.
Most likely, at some point in the past, you had to jump start the car or struggled starting the engine.
#61 would be triggered if the FSR +B voltage was below 8V during the initial check mode or below 10V while w/speed sensor above 6mph.


To be sure, recommend the following.

1. Clear the ABS error code using the above method.
You will need to follow the specific sequences using the three items.

The English version of the Workshop manual can be downloaded through NSX Prime but missing some of the pages or pages not in order.
Please note that you need the one for 00+ spec for the upgraded ABS.

Anyone with the ABS upgrade loom supplied through me should have received the Loom Installation manual including the error code reset procedure above.

2. Clear the TCS error code.
You have the DBW 95+ model so clearing the TCS error code is different from the 91-94 method.
Remove the 7.5A CLOCK fuse for your case.
Please note that this will also reset the ECU so best not to do so just before the MOT.

3. Carry out test driving.
Very likely that you have open circuit on the FL w/speed sensor that you may trigger the ABS light immediately or the light may stay On after IGSW P2 On.

With the open circuit w/speed sensor, TCS light should be triggered almost immediately after start driving.

4. Read the error code again for both the ABS and the TCS.
This time, you should only see ABS #13 and no more #61 or #15.
TCS should be the same as before and just the #4-2.

If not, further diagnosis required.


Kaz

[PeterW]

Great. Thanks Kaz,

I followed your procedure but haven't cleared the TCS error code as my MoT is coming up. As you predicted, I now have ABS #13 and TCS #42, so it's the FL wheel sensor.

The troubleshooting guide in the FSM suggests checking whether the resistance of the sensor is between 750 and 1200 Ohms. Is there any point in doing that? Also continuity to the control unit which means dismantling part of the dash. Worth to do?

Are there any watch outs for sourcing a replacement? RockAuto have them for £240 including shipping.

[Kaz-kzukNA1]

Since your failure mode is open/short circuit, it's fairly easy to diagnose.

However, you will spend much more time trying to access the FL speed sensor connector….
Depending on the temperature, the resistance would be around 800ohm.

I won't bother checking the continuity between the sensor connector and the ABS modulator before testing the sensor itself.

£240 for the w/speed sensor….
That's quite expensive but may be you need it fast???

Haven't ordered one recently so don't know the latest but from Japan, should be around £150 including the delivery/import tax.
Please check with the usual like Mita, amayama, etc.

OEM FL sensor is 57455-SL0-020.

Due to oxidation, quite often, the sensor head could stuck inside the knuckle.
However, front side is easy as the hub can be separated from the knuckle.
You can then punch it out and clean the oxidation.

Rear side is a different story if the sensor got stuck.....


Kaz

[PeterW]

Thanks Kaz,
Yes, getting at the connector behind the fuse box was interesting, especially as I wasn't familiar what to push or pull to get the connector apart. Anyway, worked it out now and for the record, the resistance measures 150 kOhms, so open circuit and this is where my problem is.
Moving on to getting the sensor out of the knuckle now.

[PeterW]

As seems to be typical, the head of the sensor broke off leaving the body seized by corrosion in the knuckle. Two bolts to get the brake calliper off and four nuts to release the hub and disc assembly and I was able drive the remains of the sensor out of the knuckle.

But what a lot of crevice corrosion there's been between the plastic body of the sensor and its hole in the aluminium knuckle. There's a rubber "O" ring which sits in a shoulder at the entrance to the hole in the knuckle and water is clearly getting past it. There's also corrosion of that shoulder and despite scraping it off, the remaining surface is lumpy and is going to let water past even more than it did when it was new. It's a poor design.

I'm going to put some silicon sealing compound on the "O" ring when I install the new sensor.

[britlude]

yup, sounds typical, the aluminium starts to corrode in the hole, grips the sensor head, then as it continues to corrode effectively jacks the mounting plate off the head, breaking the wires... undo the 2 bolts, the mounting plate falls off, sensor still firmly stuck in the hole!! been there, done that!...

reassemble with liberal use of waterproof grease!!!! :)

[PeterW]

I guess the grease will help when the water gets in, but maybe it's better to stop the water getting in in the first place? I'm thinking about a very small amount of sealing material or non hardening gasket compound on the "O" ring and around the outside of it. I'll let you know in 20 years if it worked!:)