Speed sensor

[3.0T91]

No problem guessing the topic o' this thread. I need a speed sensor. After countless ECU resets, minimal driving (b/c it's virtually undrivable), and troubleshooting with my jumper wire, I found code 42, which is for the speed sensor. So I need a new one, or a fix for the 20-year old one that's on there now. Anything would be appreciated. Mods: If you feel this thread needs to be moved to the marketplace, I won't object. But I digress. Additionally, since going MAFT, the car will only rev up to about 2700 rpm and then fuel cuts. It also does not like excessive throttle inputs, and the response sucks hind end. The MAFT is set up as per the directions on the idriders.com page that HottScennessy recommended to me. So any help on that front would be ideal. So you know, i'm on a 62-1 turbo with 4" intake pipe and the MAF mounted between the covers. I'm on an e-manage, stock 440s, and the LIPP FPD eliminator. Hope that helps. Happy driving to all!

 

[Nick M]

After countless ECU resets,

Never read that before. Pulling the EFI fuse does not fix a car.

 

[cjsupra90]

The speed sensor is built into the speedo head unit in the dash. the only way to get one is to buy a new speedo. Its a small magnetic reed switch. You might be able to get one from a salavage yard. Its been a long time since I had a MKIII speedo apart, but I think that you can remove/replace the switch itself.

Before you do all that though, if you haven't already, check continuity between the speed sensor wire at the instrument cluster and the ecu just to rule out any problems with wiring cause the likelyhood of the switch going bad is slim, unless the rotating magnet has lost significant flux strength.

 

[starscream5000]

I've never heard of someone needing to replace a speed sensor in our cars. Now speed cables is a different story (been there and done that a couple weekends ago). I guess there's a first time for everything though...

 

[3.0T91]

Already did the speedo cable, and btw, the reason I reset the ECU was to make sure it didn't throw the code accidentally.

 

[3.0T91]

I have a spare speedo, but it's for my 87. Can I remove the sensor and put it into the back of my 89 speedo, or is the speed sensor built into (not removable from) the speedometer? Any input would be appreciated.

 

[cjsupra90]

Like I said, I cant recall if they are removable, but I think that they are. They should be the same between the two.

Here is a link on how to test the sensor. I would test it first cause I have never heard of one going bad and it only requiers the cluster to be removed to do so. I would hate to pull apart the speedo head unit only to find that there is nothing wrong with the sensor.

http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?Section=BE&Page=84

 

[3.0T91]

Hmm, very interesting. So it's integral to the cruise control system, no? Makes sense I suppose, and I'm in training to be a professional GM parts changer (err, technician). Oh well, every day I learn something new about the Supra. Thanks.

 

[cjsupra90]

The speed sensor is its own entity, but outputs to several systems, Cruise, TCCS, PPS, and IIRC TEMS.

 

[wardog]

since we are in the topic of speed sensors and speedo cables....i recently installed a speedo cable and im 5mph more than other cars.....anybody has this problem....also noticed cruise control goes on and off when i use it....

 

[3.0T91]

Interesting, but yet again, makes perfect sense. Use one sensor for anything that needs a speed signal in DC (ABS sensor signals are AC due to their means of gathering the signal, IIRC).

 

[cjsupra90]

Yes, correct about the ABS and being an AC sinewave format voltage. A digital signal would be better, but its cheaper and easier to use a VR (veriable reluctance) sensor and an A/D converter in the ABS ECU for the ABS insted of a Hall Effect or something of that nature that would output a digital signal to begin with. For the regular speed sensor (where accuracy is not as important as with ABS) a basic magnetic reed switch works great and is cheap and easy and gives the digital output needed so there is no need for and A/D converter an circuitry within an ECU.

Dont get this confused though with modern electronic speedo's as the speedsensor for them is either a VR type or a Hall Effect type.

 

[3.0T91]

That's exactly right. Man am I glad I don't post on SF anymore.

 

[3.0T91]

OK so i replaced my speed sensor and I'm not throwing code 42 anymore. But guess what? I'm throwing 24 and 31 (two of my favorites). I think it has to do w/how my MAFT is set up, and I still don't know why it's cutting fuel at 2900 rpm. . .