Help! Check engine light without a code?

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Help! Check engine light without a code?

Postby Nickzendar » Thu Sep 10, 2020 11:07 pm

I received a check engine light while driving last summer that I thought was linked to me needing to replace the distributor cap and rotor. Then the light went away but when I started driving it again this summer it came back. I assusemed it was caused by the old fuel. But even after putting fresh fuel in the problem continued so I swapped plugs hopeing that would be the fix. Based on the way the car was behaving I always had an assumption as to what was the problem and never thought to check the codes to be sure. When I checked the code all I got was a code 42 which I knew was a probelm becasue it broke like 3 years ago not long after I bought the car. The light is on but go away and come back during driving. When I get into boost it will go away but as soon as im out of boost it comes back. While idleing it will sometimes go away after a while as well. After some hard driving last night it began to buck (power/fuel cut mid pull) during boost. After letting it sit for a while and then driving it home I did a pull to see if it was still doing it and it didnt buck again. The car also died twice during my test driving last night. It had a full tank of gas. Could it be my fuel pump? but if that were the case would the car not detect a lean situation and store that as a code? I need to get and install a boost and afr gauge I have just put it off becasue I didnt think I was going to get to drive this car this "summer"
Its a 1992 celica turbo 4wd with around 220,000kms
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Re: Help! Check engine light without a code?

Postby underscore » Fri Sep 11, 2020 2:29 am

The diagnostic systems in these cars is very, very basic and can only detect a handful of problems. If you're concerned about fueling how old is the fuel filter?
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Re: Help! Check engine light without a code?

Postby FC Zach » Fri Sep 11, 2020 1:12 pm

Nickzendar wrote:The car also died twice during my test driving last night. It had a full tank of gas. Could it be my fuel pump?


Mine did this a few times before I found that it was my fuel pump relay (common issue on these cars). Next time this happens, try bypassing the relay in the diagnostic box. . . (I think it's Fp and B+).
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Re: Help! Check engine light without a code?

Postby Nickzendar » Fri Sep 11, 2020 4:38 pm

underscore wrote:The diagnostic systems in these cars is very, very basic and can only detect a handful of problems. If you're concerned about fueling how old is the fuel filter?

I have no idea when the fuel filter was last done if ever. I was waiting till I had it back on the road before booking it in. Its going in next week. I can see how that might help but from what I have described does that sound like a fueling issue?
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Re: Help! Check engine light without a code?

Postby Nickzendar » Fri Sep 11, 2020 4:40 pm

FC Zach wrote:
Nickzendar wrote:The car also died twice during my test driving last night. It had a full tank of gas. Could it be my fuel pump?


Mine did this a few times before I found that it was my fuel pump relay (common issue on these cars). Next time this happens, try bypassing the relay in the diagnostic box. . . (I think it's Fp and B+).


I actually already have the bypass in my car becasue the low power mode for my fuel pump was no longer working well and would make my car run very rough at idle.
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Re: Help! Check engine light without a code?

Postby underscore » Fri Sep 11, 2020 6:55 pm

There are a few possibilities, but it's always best to start with basic maintenance items when trying to sort out problems.
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Re: Help! Check engine light without a code?

Postby Nickzendar » Fri Sep 11, 2020 10:38 pm

underscore wrote:There are a few possibilities, but it's always best to start with basic maintenance items when trying to sort out problems.

True. Thats what caused me to fix all that other stuff. The problem is if the fuel filter does not fix the issue I have no idea where to even start looking to try and fix it. I had a friend suggest it could be the tps but my throttle response does not seem irregular. I have tried to look for a replacement tps online and haven't found anything which is unfortunate.
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Re: Help! Check engine light without a code?

Postby 93celicaconv » Sat Sep 12, 2020 11:22 am

Is your 92 ST185 a Canadian market version?

On USDM ST185's, DTC #42 is a fault with the vehicle speed sensor signal. It trips when there is no vehicle speed sensor signal for 8 seconds when the engine speed is between 2,500-5,000 RPM and the coolant temp. is below 80 deg C (176 deg F), except when racing the engine.

You may have a different fault associated with DTC #42 on yours if yours was built for a different market than the US.
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Re: Help! Check engine light without a code?

Postby Nickzendar » Sat Sep 12, 2020 6:21 pm

93celicaconv wrote:Is your 92 ST185 a Canadian market version?

On USDM ST185's, DTC #42 is a fault with the vehicle speed sensor signal. It trips when there is no vehicle speed sensor signal for 8 seconds when the engine speed is between 2,500-5,000 RPM and the coolant temp. is below 80 deg C (176 deg F), except when racing the engine.

You may have a different fault associated with DTC #42 on yours if yours was built for a different market than the US.

Yes mine is a canadian market car. The speed sensor fault makes sense tho becasue my speedo does infact not work.
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Re: Help! Check engine light without a code?

Postby 93celicaconv » Sat Sep 12, 2020 6:40 pm

That's interesting. I say that because on North American ST185's, the signal from the speed sensor is electronic, but the signal going to your speedometer is mechanical (cable). The adapter assembly on the transmission does both. Sounds like both your electronic and your mechanical outputs are not working. Given that, I would be thinking your driven gear or drive worm on your transmission is broken. The driven gear is easy to replace. The drive worm I believe requires the transmission to be taken apart.

I think I would be focusing on this area, if it was me. Shouldn't be too hard to find out if your driven gear is broken.
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Re: Help! Check engine light without a code?

Postby Nickzendar » Sun Sep 13, 2020 5:02 am

93celicaconv wrote:That's interesting. I say that because on North American ST185's, the signal from the speed sensor is electronic, but the signal going to your speedometer is mechanical (cable). The adapter assembly on the transmission does both. Sounds like both your electronic and your mechanical outputs are not working. Given that, I would be thinking your driven gear or drive worm on your transmission is broken. The driven gear is easy to replace. The drive worm I believe requires the transmission to be taken apart.

I think I would be focusing on this area, if it was me. Shouldn't be too hard to find out if your driven gear is broken.

How easy would it be to spoof the sensors signal? Like could I just give it a constant voltage to make it look like the sensor is working or would that mess something else up?
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Re: Help! Check engine light without a code?

Postby 93celicaconv » Sun Sep 13, 2020 11:25 am

In my opinion, it would be a lot easier and better if you checked what the actual problem is and corrected it. If the driven gear is stripped, the effort to replace it is minor. One would have to check why it stripped though. If the speedometer mechanical cable is bound tight, then that would need to be resolved. If you find you need a new speedometer driven gear, it appears to be still available through Toyota, even eBay (https://www.ebay.com/itm/3340319406-Gen ... 2978954867).

I would think you would have difficulty replicating the speed output signal to something the ECU could interpret. And with it not changing speed while the engine does, I would think that also would lead to problems.
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Re: Help! Check engine light without a code?

Postby 2000twincamturbo » Sun Sep 13, 2020 6:47 pm

Ive had that happen to me once also about five years ago. Turns out it was a blown capacitor in my ecu. im not saying thats whats happening with your car but its super easy to check and worth ruling it out.
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Re: Help! Check engine light without a code?

Postby Nickzendar » Sun Sep 13, 2020 8:05 pm

93celicaconv wrote:In my opinion, it would be a lot easier and better if you checked what the actual problem is and corrected it. If the driven gear is stripped, the effort to replace it is minor. One would have to check why it stripped though. If the speedometer mechanical cable is bound tight, then that would need to be resolved. If you find you need a new speedometer driven gear, it appears to be still available through Toyota, even eBay (https://www.ebay.com/itm/3340319406-Gen ... 2978954867).

I would think you would have difficulty replicating the speed output signal to something the ECU could interpret. And with it not changing speed while the engine does, I would think that also would lead to problems.

Is there a break down on here on where and how to remove the driven gear and stuff.
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Re: Help! Check engine light without a code?

Postby 93celicaconv » Sun Sep 13, 2020 9:51 pm

Nickzendar wrote:
93celicaconv wrote:In my opinion, it would be a lot easier and better if you checked what the actual problem is and corrected it. If the driven gear is stripped, the effort to replace it is minor. One would have to check why it stripped though. If the speedometer mechanical cable is bound tight, then that would need to be resolved. If you find you need a new speedometer driven gear, it appears to be still available through Toyota, even eBay (https://www.ebay.com/itm/3340319406-Gen ... 2978954867).

I would think you would have difficulty replicating the speed output signal to something the ECU could interpret. And with it not changing speed while the engine does, I would think that also would lead to problems.

Is there a break down on here on where and how to remove the driven gear and stuff.

Not that I am aware of.

If you follow your speedometer cable on the engine bay side of the firewall, you will see where it connects near the transmission. You will just need to disconnect your speedometer cable assembly where it attaches to the electric speed sensor. In fact, one you disconnect the mechanical speedometer cable, you should try turning the piece of the speedometer cable extending out of it and see if it turns freely. If it does, then with all 4 wheels off the ground, turn your rear propeller shaft and see if the inside of the speed sensor turns. If it does not, you more than likely have a broken driven gear.

Does someone on this forum know of a thread stating the process associated with checking the speedometer driven gear to see if it works for the OP here in this forum?
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