Intermittent code 42 (Vehicle Speed Sensor) *FIXED

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Intermittent code 42 (Vehicle Speed Sensor) *FIXED

Postby FC Zach » Sat Oct 06, 2018 6:59 am

Specs on my car:
-1992 with stock ECU
-Cruise control works
-Speedometer/Tach works
-ABS works (last I checked a few weeks ago)

Recently, my CEL has started to illuminate briefly and randomly upon start-ups and while driving. . not sure if it has anything to do with it but while driving it seems to happen after being on and then followed by a sudden off throttle (enough that the blow-off sings), a second or more after that the CEL illuminates and goes away. This is what baffles me because that seems completely unrelated to the light and more like an engine issue.

I replaced the sensor for the cruise control years ago and it works fine (not entirely sure if this is even tied to the ECU anyways, if it was why didn't it do this before replacing it?), speedometer works fine too. Would the hub sensors for the ABS cause this? While searching for a possible cause, I recall seeing a mention of these somewhere and to check them with an ohm meter.

I haven't tried disconnecting the battery yet as I was hoping it would just stop (and mostly because I don't want to reset my radio) but it has been a few days now. If any of you have experienced this, what do you suggest?

Thanks in advance
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Last edited by FC Zach on Wed Oct 17, 2018 3:16 am, edited 1 time in total.
1992 Toyota Celica AllTrac
1987 Mazda RX7 Sport
1979 Yamaha G1A, rotary powered with Sachs KM24
1976 Hercules W2000, oil injected
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Re: Intermittent code 42 (Vehicle Speed Sensor)

Postby underscore » Fri Oct 12, 2018 3:05 pm

You should be able to reset the ECU without disconnecting the battery, just pull the EFI fuse.

I had this code popping up randomly on my car as well, I don't think it looks at the ABS sensors at all as mine are all removed and the code was still intermittent. I did end up replacing the speed sensor which seems to have cleared it up, though it could just be a dirty connection or loose wire. Since yours seems to happen at a time when the engine is getting a big jolt (on start amd dropping off throttle) I'd suspect either the impact is jarring the sensor enough to mess it up or the movement is flexing a wire with a break in it that's causing a momentary loss of connectivity.
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Re: Intermittent code 42 (Vehicle Speed Sensor)

Postby FC Zach » Fri Oct 12, 2018 3:24 pm

Thank you! I forgot about isolating just the ECU via the fuse. . I'm gonna try that as well as check for a bad connection.

I thought the speed sensor was for cruise only. . So the ECU feeds off this sensor too?
1992 Toyota Celica AllTrac
1987 Mazda RX7 Sport
1979 Yamaha G1A, rotary powered with Sachs KM24
1976 Hercules W2000, oil injected
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Re: Intermittent code 42 (Vehicle Speed Sensor)

Postby underscore » Fri Oct 12, 2018 3:31 pm

My car doesn't have cruise but since it's from Japan the ECU has a speed cut at 180km/h which would need it. I think they all have the speed tied into the ECU for part of the TVSV control (using the speed + RPM to determine which gear you're in) but I may be wrong.
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Re: Intermittent code 42 (Vehicle Speed Sensor)

Postby FC Zach » Fri Oct 12, 2018 3:37 pm

Ten four, thank you!
1992 Toyota Celica AllTrac
1987 Mazda RX7 Sport
1979 Yamaha G1A, rotary powered with Sachs KM24
1976 Hercules W2000, oil injected
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FC Zach
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Re: Intermittent code 42 (Vehicle Speed Sensor)

Postby FC Zach » Tue Oct 16, 2018 2:21 pm

This issue has continued for about two weeks now but a day or two ago the CEL started to brighten and dim like the low fuel light so with that new evidence, I suspected the ECU. . This morning I pulled the ECU connections to temporarily connect my spare (with a ground wire between the chassis and ECU) and went for a test drive. All went well, drove about ten miles.

Once I got home I removed the ECU and permanently installed the "spare". . it was actually the original but failed due to capacitors leaking 5 years ago and has since been repaired. After that, I opened up the one I pulled and sure enough the culprit was leaky caps. . now to find the extra caps I ordered years ago to repair the original.

Image

Image
Last edited by FC Zach on Tue Oct 16, 2018 5:28 pm, edited 1 time in total.
1992 Toyota Celica AllTrac
1987 Mazda RX7 Sport
1979 Yamaha G1A, rotary powered with Sachs KM24
1976 Hercules W2000, oil injected
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FC Zach
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1992 Toyota Celica

Re: Intermittent code 42 (Vehicle Speed Sensor)

Postby FC Zach » Tue Oct 16, 2018 2:25 pm

I took pictures of the original ECU when it failed years ago and coincidentally they have the exact same leaky caps.
1992 Toyota Celica AllTrac
1987 Mazda RX7 Sport
1979 Yamaha G1A, rotary powered with Sachs KM24
1976 Hercules W2000, oil injected
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FC Zach
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Posts: 1026
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1992 Toyota Celica

Re: Intermittent code 42 (Vehicle Speed Sensor)

Postby underscore » Tue Oct 16, 2018 4:32 pm

Did you replace all the caps? I've been meaning to swap them out in my spare ECU but I haven't had the time to open it up and look up all the specs to order them.
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It's for sale! http://www.alltrac.net/phpBB2/viewtopic.php?f=64&t=52181
Build thread http://www.alltrac.net/phpBB2/viewtopic.php?f=44&t=44216
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Re: Intermittent code 42 (Vehicle Speed Sensor)

Postby FC Zach » Tue Oct 16, 2018 4:54 pm

No, just the two 10uf50v caps. I haven't replaced any others, just the failed ones. If it helps any, I got a really good deal for caps on eBay. . More than I'll ever need (hopefully) for a few bucks. Luckily it was a bulk pack because I would have never guessed two ECUs would have had the exact same caps leak.
1992 Toyota Celica AllTrac
1987 Mazda RX7 Sport
1979 Yamaha G1A, rotary powered with Sachs KM24
1976 Hercules W2000, oil injected
User avatar
FC Zach
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Posts: 1026
Images: 9
Joined: Mon May 20, 2013 7:43 am
Location: Eagleville, TN

1992 Toyota Celica

Re: Intermittent code 42 (Vehicle Speed Sensor)

Postby FC Zach » Tue Oct 16, 2018 5:03 pm

1992 Toyota Celica AllTrac
1987 Mazda RX7 Sport
1979 Yamaha G1A, rotary powered with Sachs KM24
1976 Hercules W2000, oil injected
User avatar
FC Zach
Established Member
 
Posts: 1026
Images: 9
Joined: Mon May 20, 2013 7:43 am
Location: Eagleville, TN

1992 Toyota Celica

Re: Intermittent code 42 (Vehicle Speed Sensor)

Postby underscore » Tue Oct 16, 2018 7:47 pm

Awesome, thanks!
★ 1991 GTFour RC ~ "Rebel Scum" ★
It's for sale! http://www.alltrac.net/phpBB2/viewtopic.php?f=64&t=52181
Build thread http://www.alltrac.net/phpBB2/viewtopic.php?f=44&t=44216
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Re: Intermittent code 42 (Vehicle Speed Sensor)

Postby FC Zach » Wed Oct 17, 2018 3:12 am

I should also add that in the last few days, the CEL started to illuminate for longer periods than before (as well as brighten and dim). I decided to check to see if more codes were present but all I got was an erratic flashing. . that's what gave me the idea that the diagnostics portion of the ECU was bad (same as my last ECU).
1992 Toyota Celica AllTrac
1987 Mazda RX7 Sport
1979 Yamaha G1A, rotary powered with Sachs KM24
1976 Hercules W2000, oil injected
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FC Zach
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Posts: 1026
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Joined: Mon May 20, 2013 7:43 am
Location: Eagleville, TN

1992 Toyota Celica

Re: Intermittent code 42 (Vehicle Speed Sensor) *FIXED

Postby 93celicaconv » Fri Oct 19, 2018 1:18 pm

I think this should be a sticky, given capacitors in early 1990's Toyotas were problematic (how many radios failed just due to this?).

But I'm confused about the pictures, which I think indicates two different capacitors in the ECU failed, and they look physically different. But the repair process consisted of using a single capacitor type for each of the two unique failed capacitors?

Lastly, in the pics, I can see the leak from the capacity shown on the horizontal circuit board, but I can't see a leak on the capacity pointed to on the vertical circuit board (which I'm interpreting to be the capacitor just below the screwdriver tip). How did you know that particular capacitor had failed? Or was there a capacitor above the screwdriver tip that pretty much disintegrated?
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Re: Intermittent code 42 (Vehicle Speed Sensor) *FIXED

Postby FC Zach » Fri Oct 19, 2018 2:06 pm

Yes, it is two capacitors. . . One is on the top board one is on the bottom board. They are both the same size (10uf 50v) caps.

I replaced both since they are a common problem regardless of whether there's any visible sign of leaking or not. . But these were leaking, you could see the board coating bubbling. I know it failed from visual inspection but on top of that, a previous experience.
1992 Toyota Celica AllTrac
1987 Mazda RX7 Sport
1979 Yamaha G1A, rotary powered with Sachs KM24
1976 Hercules W2000, oil injected
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FC Zach
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Posts: 1026
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Joined: Mon May 20, 2013 7:43 am
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1992 Toyota Celica


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