speedo/cluster repair problem

[hkz286]

Hello all,

I’ve had an issue with the brake warning lamp on my car since I bought it. Having grounded out the rear taillight pin as per the service manual, the lamp remained on. So I figured it was the cluster/dash that was at fault and upon looking at other people’s cars, it looked as though the capacitors leaked over the chip that controls the warning lamps.

I contacted kaz to see if he would repair it, and whilst he said he would, he also said that the tacho and speedo will probably be out of calibration afterwards so would need recalibrating. The only people I can find who do this is T3TEC in Japan. As I don’t speak Japanese and I don’t know anybody in japan, I thought this option was problematic.

However, having looked over a few post, it seems that there have been a few fires in regards to the capacitors leaking, and whilst unlikely, it still worried me. I thought I may as well go ahead and replace the capacitors to eliminate the risk of a fire, and made peace with the fact the warning lamp would still be on, and the speedo and tach will not be correct (but I won’t be set on fire )

So I go ahead and replace them all with the correct spec and clean off all the damage done by the leaking capacitor (there was only one).

Put everything back together, switch it on and suddenly the temperature gauge suddenly goes to maximum. Now the speedo and tach are working perfectly (verified with gps and external rev counter) which is more luck than judgment and the warning lamp is still on (the chip must have been damaged) however the temperature gauge is all wacky.

Now I went about this very carefully, one at a time, verifying the polarity of each capacitor and the spec and replacing one by one. However I will be taking it apart again to double check I haven’t done anything silly.

Before I do this does anyone have any idea why the temperature gauge would always sit at maximum after I changed the capacitors? I know the calibration of things could be out because of the tolerance of the capacitor but I didn’t think it would be this dramatic.

Any help would be appreciated.

mike

 

[Old Guy]

First off, rule out the easy stuff. Pull the connection to the coolant sensor on the engine. Power up the ignition and the gauge should read cold. If the gauge pegs on hot then you have confirmed that the problem is not with the sensor.

The coolant sensor goes from high resistance when cold to low resistance when hot. The fact that your gauge is pegging on hot suggests that there is an unplanned ground somewhere on the connection to the temperature sensor that is causing the gauge to measure a low resistance. The unplanned ground could be a failure in the vehicle wiring harness or more likely, you might have shorted out the sensor connection on the circuit board with some solder splash when you were replacing parts. I don't know whether the temp gauge is a magnetic type or bimetalic type (I expect bi metallic); but, I don't expect that there are any capacitors in the circuit so the gauge problem is probably not directly capacitor related.

Once again rule out the easy stuff. With the gauge assembly disconnected and the temperature sensor on the block disconnected, use a multimeter to check for a ground on the connection between the sensor and the cluster. With everything disconnected at both ends, the resistance measurement should show open circuit. If not, then you have a short somewhere on that wire. If it reads open circuit (which would be normal) then you likely have a short directly on the gauge cluster circuit board. You will have to examine the traces on the board around the fuel gauge assembly to look for damage.

The basic NSX shop manual has basic details on the gauge assembly and testing. I know that there is a separate detailed NSX electrical service manual that has more stuff in it than the basic shop manual. I don't have one of these manuals; but, if you can latch on to one it might provide more details on the layout and testing of the instrument cluster.

With respect to the Brake Lamp indicator remaining lit on you car, it would seem unlikely that is a safety indicator problem if none of the other lights on the indicator are lit up and still function correctly (driver's door, trunk, ....). When you do the ground check on the pin in the 8 pin connector on the harness that connects to the right tail light failure sensor, a faulty Brake Lamp indicator or an open circuit in the wire between the 8 pin connector and the instrument cluster can cause the Brake Lamp to remain lit. You need to rule out an open circuit before concluding that the indicator is faulty. Also, be aware that there is a discrepancy in the service manual with respect to the brake lamp indicator circuit. The wiring diagram (and the pin out for the safety indicator plug) cluster shows an orn/wht wire going from the instrument cluster to the 8 pin connector on the right failure sensor. The test procedure refers to grounding a wht/grn wire. According to the wiring diagram there are no wht/grn wires in the connector; but, there are grn/wht wires in the connector which are the wrong wires to test. Make sure that you tested the correct wire when you did that test. That error exists in the 1991 manual and remains in the later 2008 manual.

 

[hkz286]

thanks for the reply,

it is indeed a broken ground. On the actual gauge itself the wire has come apart from the post. Trouble is the post is used for the mounting the gauge, and the entire thing has become brittle and cracked with age. Therefore when i tightened the screws, the post rotated, pulling the wire loose from the copper windings on the gauge. I could solder the wire back in place but have no way of securing the gauge. Im going to need a new gauge now i think.

thanks for the suggestions

 

[Boneinfilet]

On that subject....somewhat. I have a yanked ABS cable from the sensor on my 02 Targa(manual trans). Happened somehow during the transport of the vehicle from the shop that I installed the engine and tranny to home. A mere mile and a half. Anyway, its rear right sensor and picking are slim my friends. The places online that claim to have them are out of stock it seems. Now I think a guy on Ebay has one, but wants 296$ for it!!! My question is 2fold. Firstly, does it have to be a cable and sensor specifically for the Rear Right side? Second, Does it have to be for the NSX, specifically? The RSX, TL, and a couple others have very similar looking sensors with the same pigtail at the end. Anyone?

 

[drew]

mods you might want to move [MENTION=37311]Boneinfilet[/MENTION] post to
http://www.nsxprime.com/forum/showthread.php/209487-NSX-Right-(Passenger)-ABD-wheel-speed-sensor

 

[Old Guy]

My moderator tools seem to have gone missing, so somebody else will have to deal with moving the post. However, as to interchangeability. The speed sensor is a simple reluctance sensor. The actual sensor part from one of the other wheels will probably work electrically as long as you get the polarity on the wiring correct. The bigger issue is will it fit. The tip of the sensor has to be positioned at the correct distance from the toothed speed wheel other wise the signal generated by the sensor may fall outside of the acceptability range for the ABS module. How you safely manage the wiring is an issue you have to deal with. Depending on the damage you may be able to reuse most of the existing wiring and just connect a replacement sensor on to the end.

A speed sensor from another car might work. The resistance of the sensor would need to be the same. With luck that would indicate the number of turns on the pole piece is the same which should generate the same signal level. However, if the gauge of the wiring is different you could have the same resistance; but, different number of turns in which case you are likely screwed. Even if the electrical characteristics of the sensors match up you still have the whole fit and positioning problems to deal with. Personally, I put this option at a low probability of having a successful outcome.

Have you tried Amayama.com or mitamotorsports.com for parts. If Amayama or Mita can't get it, it probably does not exist. If Amayama has it it can be delivered fairly quickly, you just have to pay through the nose for shipping.