Traction Control System Code 4-9 (All Wheel Sensor)

[tbox]

Hey everyone, I'm looking for some help on a TCS issue on my 93 MT. The previous owner removed and sold the TCS module, so I sourced another 91-94 TCS module (P/N 39900-SL0-013) and had just recently plugged it in along with the ABS/ALB module (P/N 39790-SL0-003). The TCS problem indicator light (and only this light) came on shortly after the car starts and stayed lit. After reading the 1991 service manual on TCU troubleshooting and shorting the diagnostic connector, I logged a TCS code 4-9 along with an ECU code 3-6.

The diagnostics for code 4-9, which points to issue with all wheel speed sensors, had me verify the wiring between four pairs of pins (presumably for wheel speed sensors at each wheel) between the TCS 20-pin connector and the ABS 18-pin connector. After doing the continuity check on the four pairs, it turned out two pins on the ABS connector side were reversed from what the manual indicated:

It's unlikely that the wires were reversed from the factory, or that the previous owner re-pinned the ABS connector, so I'm asking help from the community to help me verify the wiring on the 93 TCS 20-pin connector and the ABS 18-pin connectors. It would be great if someone can show the same continuity check diagram with the pin pairs from a 93-specific service manual that so we know if the correct pin wiring. Hope

And yes, I did search, but no one else seemed to have the same reversed wiring problem I'm experiencing:

http://www.nsxprime.com/forum/showthread.php/146027-TCS-ABS-lights-on-together-weird-trouble-code
http://www.nsxprime.com/forum/showthread.php/95384-AntiLock-and-TCS-light-coming-on-why
http://www.nsxprime.com/forum/showt...s-on-stumbling-and-climate-control-won-t-work

Any help is appreciated!

 

[Kaz-kzukNA1]

There are many mistakes in the workshop manual but for this one, it looked to be fine and I think you just got confused with how Honda uses different drawings on the wiring diagram.

For the clarification, I’m using the following term as follows;

Unless otherwise notified, Honda will show the wiring diagram looking into the connector from the terminal side.

For the Connector shape;
Plug: single line box, when talking about the controller unit, almost always this is the connector on the loom side.
Socket: double line box, when talking about the controller unit, almost always this is the one built in to the unit.

For the Terminal shape;
Male
Female

So, in your copy of the workshop manual, the TCS 20pin connector is shown as single line box so it’s the Plug and thus, it’s the connector on the chassis loom side and we are looking into the female terminal side.
You interpreted this correctly when numbering the #7 and #9 terminal in your photo because you are looking from the wire (back) side of the connector.

On the other hand, the ABS 18pin connector is shown as double line box so it’s actually the Receptacle connector built into the ABS controller unit and we are looking into the male terminal side.

So, by now, you probably understood the mistake.
The orange connector in the above photo is the Plug one on the chassis loom side and you are looking from the wire (back) side.
This is in effect the same as looking into the Receptacle connector on the ABS controller with the male terminal and thus,
you don’t mirror the pin # of the diagram in the workshop manual like you wrote in the photo for #14 and #15.

May not be easy to see in this photo but you should be able to see where the ORN/BLK wire is and also hint of red line at the upper section (in this photo)
of the wire sleeve where the ORN/RED wire should be and thus, the ORN/BLK and ORN/RED wires on your NSX are at the correct position as per the manual.


For your reference, all 4 wheel speed raw signals will first enter the ABS controller.
Then, they are filtered and level converted before being passed to the TCS controller.
Therefore, unless you saw ABS warning light as well, your issue is not at the wheel speed sensor but something else.
In fact, very rare to lose all 4 signals at the same time so probably wiring issue, etc.


Kaz

 

[tbox]

Wow! Thank you for providing a quick and extremely thorough response, [MENTION=25737]Kaz-kzukNA1[/MENTION]. (If only people at work would respond to my e-mails this way!) It's great that you pointed out the connector drawing convention, since I actually had never noticed that they drew single and double lines to distinguish between plug and socket sides...I should've gone back and read all the instructions. Lesson learned!

And thanks a million for the perfect connector picture. Hope you didn't have to crawl into the car just to take it So according to your picture, my ABS connector wiring is correct. If this is the case, why did the other two pairs (18/6 & 20/5) pass the continuity check even though I had incorrect assumptions for the pins? I'll have to go back and verify them again...hopefully this will lead somewhere.

Regarding the note about the speed sensor signals first entering ABS and then gets passed to the TCS, does that mean TCS will not function (and/or prohibit the vehicle from driving properly) if TCS module is connected and ABS module is not connected?

 

[Old Guy]

Regarding the note about the speed sensor signals first entering ABS and then gets passed to the TCS, does that mean TCS will not function (and/or prohibit the vehicle from driving properly) if TCS module is connected and ABS module is not connected?

The TCS will definitely not function - a missing ABS module or no connection between the TCS and the ABS means that the TCS is not getting any wheel speed measurements. What do you mean by driving properly - that the TCS is trying to implement active traction control because it is in failure mode? Unfortunately, I have a 1998 service manual which is based upon the drive by wire so I can't check the details of the 1993 version; but, I expect that the absence of all 4 wheel speed signals should cause the TCS to shut down and not implement any control actions.

 

[Kaz-kzukNA1]

................... So according to your picture, my ABS connector wiring is correct. If this is the case, why did the other two pairs (18/6 & 20/5) pass the continuity check even though I had incorrect assumptions for the pins? ...........................

That’s because whoever scanned the document had some issues as you can see misalignment at the text, line, diagram, etc.
The connection in the above diagram seemed to be edited or misleading.

The correct connection is;
TCS 20P #18 – ABS 18S #5
TCS 20P #20 – ABS 18S #6 .

If you flip back a page on the service manual and look at the diagram on page 19-119, you will see the correct diagram.

Regarding the note about the speed sensor signals first entering ABS and then gets passed to the TCS, does that mean TCS will not function (and/or prohibit the vehicle from driving properly) if TCS module is connected and ABS module is not connected?

Your assumption is almost correct.
The w/speed sensor is only connected to the ABS controller and thus, the raw signal is first processed there.
Inside the ABS, it will carry out signal conditioning, amplified and level converted before passing the signal to the TCS controller.

Therefore, if ABS controller is absent or not powered up, TCS won’t receive the required signal and thus, it will trigger the TCS warning light.

When you turn the IG key into P2 On position, both the ABS and TCS lights should stay ON until you start the engine.
Before starting the engine, if you don’t see the ABS light but just the TCS, ABS controller is not powered up or ABS light bulb is dead.


On non-DBW model, there is serial comm link between ECU and TCS.
ECU is always the master device and if TCS warning light is triggered, TCS will stop its feature and the ECU will just behave as if there is no TCS controller and won’t be affected.


Kaz

 

[tbox]

Thanks to insightful comments from @Kaz-kzukNA1 and @Old Guy, I was able to narrow down the problem and finally resolve the issue.

The wiring was perfectly fine. The diagram from pg 19-121 of the scanned manual was indeed incorrect. The correct pairing can be found in the text instruction boxes, and are as Kaz had mentioned:

TCS 20P #18 – ABS 18S #5
TCS 20P #20 – ABS 18S #6
TCS 20P #7 - ABS 18S #14
TCS 20P #9 - ABS 18S #15

So my wiring wasn't the problem, and it's very unlikely for the TCU and sensors were faulty (I also checked that all my sensors were there). Following the comments, I narrowed the culprit to the ABS and noticed that the ABS indicator light did not light up in accessory mode, to which the service manual suggested on pg 19-44:

1. Check for blown ABS indicator bulb
2. Open circuit in YEL wire between No. 5 (10A) fuse and gauge assembly
3. Open circuit in BLU/WHT wire between gauge and ABS module
4. Loose component grounding of the ABS module to the body

I first verified that the ABS indicator bulb was not blown. Out of the other 3 options, open circuits in the wiring harness was not a very common occurrence, so there's a good chance that it was grounding.

Since my ABS module was removed from the bracket, for awhile it was dangling in the passenger footwell behind the carpet. I remember my ABS light flashing on and off when the car accelerated, suggesting that there's some sort of intermittent continuity. Thinking back, that made sense if the ABS module needed to be electrically grounded to the chassis to function.

Before I arrived at this conclusion, I had been diagnosing the test with the ABS module connected but resting on top of the carpet, which acted as an insulator. After I touched the metallic case on the aluminum body and turned on the car, the ABS indicator light came up and then disappeared, along with the TCS light. I then bolted the ABS module to the original bracket and then the bracket to the body, and started the engine. Both ABS and TCS light came on and went away. Problem solved!

A huge thanks to everyone who posted for the help! Hopefully this thread will help folks who might run into the same problem in the future.