TCS light. Harbinger of future problems?

[nsx_2k]

I recently encountered an unusual problem with my stock '91 NSX w/ 106K miles. The car has everything stock (including wheels/ties) with no aftermarket components. I was returning from a weekend drive with friends. During our drive, I did activate VTEC multiple of times and overall had a very enjoyable drive. For reference, I never race my vehicle for I have another vehicle for such purposes, so the car was not beat upon with any sort of drag racing. During the drive home while I was cruising at ~50MPH, the yellow TCS light came on. This is the TCS failure light, not the activation one. I found a safe place to pull over, shut the car down and restarted the car. The TCS light was then extinguished. Upon returning home, I researched the issue and there were some posts referencing that you should pull the codes for there may be other issues. Armed with the workshop manual, I pulled the codes and they are listed below. In order to ensure that I had them written correctly, I rechecked at least 4 times cause they simply didn't make sense. What is interesting was the CEL flashed codes as well; however, never before had I seen the CEL come on during engine operation.

Error codes:

TCS:

2-1: Steering Wheel angle sensor
3-4: Abnormal Voltage ref signal


ECU:
21: Front spool solenoid valve
51: Rear spool solenoid valve
36: TCFC Signal

I cleared the codes per the workshop manual and took the car for another spirited drive the next day. I activated VTEC a few times as well. During my drive there was no unusual behavior from the car. When I returned home, I attempted to pull codes and nothing! Now don't get me wrong, I'm delighted that no codes resurfaced; however, I'm wondering if there is an occult problem lurking with my car that may surface at a later time. The error codes don't seem to make any sense to me for they don't seem to be related. Could this be a brown-out scenario caused by a failing relay? I simply don't know. Any thoughts?

 

[NSX2398]

You might think that having the TCS light come at the same time as the CEL would be a common problem that someone would have come across before. But if you searched you'll find that multiple people (including me) have had this situation in the past and the reasons are all over the map because there are so many combinations because the two modules interact on so many things. Have a look in the shop manual and there is a whole section which helps you narrow it down. You might also want to pull the clock fuse for 15 seconds (while car not running) and then replace it .. which clears the codes so you're not dealing with some previous problem. Unfortunately, the TCS and ECU are two of the more expensive parts to replace (I did both) so take your time and follow the flowcharts and get it right. Good luck.

 

[jwmelvin]

This does strike me as possibly low voltage. The TCS light very commonly appears with the CEL/MIL light, for seemingly little or no reason. Don't freak out. Yet.

 

[Old Guy]

jwmelvin may be correct. Temporary low voltages (or less frequently high voltages) on the sensors can cause the ECU and other electronics to interpret the abnormal voltage as a sensor problem. Usually generates some kind of out of range or sensor error problem. The reference voltage that is used on the sensors is typically around 5 volts and is provided by an internal regulator in the electronic device. As a result, your battery voltage (12 v) could be just fine and you could still be having a sensor reference voltage problem. If (and that is a big if) this is the problem, it is likely due to a poor connection someplace rather than an actual failure in the electronic bits (if the regulator fails you will know it because the car will be dead in the water).

As Ian notes, the TCS and ECU are interconnected, so a problem starting in one place can have unintended consequences. As Ian also suggests, its worth looking at the trouble shooting procedure in the service manual; however, until the problem re emerges you really can't do any trouble shooting. As jwmelvin suggests, don't panic, the problem may never re emerge. If you feel the need to do something preventative and minimally invasive, you could start checking the condition of the wiring and connections which is probably a good idea on a car that is approaching 25 years of age. As these cars get older, I expect that it may be the deterioration of the sensors and sensor wiring rather than mechanical bits that become an Achilles heel.