Jump to content

Check Engine Light

drl911

By drl911
in Ask A GM Technician

Recommended Posts

drl911 New Member

drl911

Posted
Posted

:chevy:

 

1993 GMC Z71 (~165,000 miles)

 

Recently the check engine light came on for the first time in my 4+ years of ownership. This truck is only driven a few times per month, but I believe at about the same time as the check engine light coming on the transmission started to not shift automatically. In fact it seems to always start out in top gear. The transmission will change gears "manually" via the gear select lever on the steeering column, but not automatically while driving. The ECU will not give any codes at the local auto parts stores. I have tried 3 different places all with the ability to read OBD1. So far I have changed the throttle position sensor with no improvement. I bought a speed sensor, but they sold me the wrong one so that has not been tried yet. Someone suggested I need to replace the ECU. Does this sound right because it will not give any codes and the electronic transmission control is not working either???

 

Thanks in advance for your suggestions,

Dan

Shav0 Enthusiast

Shav0

Posted
Posted

I had a similiar problem in a 02 elantra. What happened was the ECU lost imput from the transmission input speed sensor and resulted to "safe mode." What safe mode is, is your transmission will automatically go into 3rd gear and stay put. This is to basically allow you to still get yourself to a garage to get it fixed, but it isn't reccomended that you drive like this for a long period of time. This problem will also illuminate the check engine light.

drl911 New Member

drl911

Posted
  • Author
Posted

Thanks for sharing your experience. This truck does drive/behave exactly as you describe the "safe mode". I am going to take back the wrong speed sensor I was sold this past weekend and hopefully get the correct one to solve the problem.

 

Thanks again,

Dan

Shav0 Enthusiast

Shav0

Posted
Posted

Im not saying thats exactly the problem, but It sounds to me like your in some sort of "safe mode." If transmission is unsure of the speed it's actually going it will cause this same thing to happen.

drl911 New Member

drl911

Posted
  • Author
Posted
Just so you know, you can retrieve OBD-I codes yourself using a paper clip. You don't have to waste gas/money taking it to the local parts shop.

 

Instructions: http://tvoffer.tripod.com/gmcodes.htm

Codes: http://www.troublecodes.net/GM/

 

 

 

 

So what does it mean if the ECU will not give a code under any circumstances (I have tried all of the above several times)? Nor will the "check engine soon" warning clear by disconnecting the battery.

 

Thanks for all of the input,

Dan

GM-Tech Senior Enthusiast

GM-Tech

Posted
Posted
So what does it mean if the ECU will not give a code under any circumstances (I have tried all of the above several times)?  Nor will the "check engine soon" warning clear by disconnecting the battery.

 

Thanks for all of the input,

Dan

 

 

 

 

 

You should at least get a code 12. Make sure you're jumping the pins AFTER the key is on. Don't jump tthen turn the key on. However, if you can't clear the check eng light, it could be a bad ECM, or you have something wrong that's setting a code the instant you turn the key on.

Archived

This topic is now archived and is closed to further replies.

Go to topic listing

  • Latest Articles

  • Posts

    • newdude
      Transmission Temperature Hitting 220s

      By newdude · Posted

      It is working as designed.  NHT and non NHT trucks have the same exact transmission cooling setup.  NHT just gets a larger radiator.     The transmission cooler loop on these is as follows.     -Transmission out goes into an oil to water heat exchanger (item #1 in the first illustration below).  This exchanger has engine coolant opposite the transmission fluid and uses engine coolant to warm and then regulate the transmission fluid temperature when its in the operating window.   - From the cooler it goes to a thermal bypass valve (item #11 in the 2nd illustration below).  If the ATF has not reached the temp to open the bypass (194F), it loops back.   - When it reaches 194F, the thermostat opens and ATF then flows out to the oil to air auxiliary cooler (item #17 in the 2nd illustration) at the front of the truck.  From there it goes back to the transmission.     Your only fix would be to swap for the PPE thermal bypass delete block which will open the loop to the aux cooler all the time.  It will STILL run warm, probably 170-200F, but that's as low as you'll get it as its still flowing through the oil to water exchanger.      
    • Grumpy Bear
      Slate Electric Truck

      By Grumpy Bear · Posted

      Most say the oil temperature needs to above the boiling point of water to rid it of moisture and long enough to dry it. Many think that is about a hour at 212 F or more. Those people have never line dried cloths in a Midwest winter. Leave a pan of water sitting on the counter and eventually it all evaporates. So heat drives the time it takes. Water in oil under 175 F, the Nitration initiation temperature, is a minimum then for temperature and samples I've done that use Karl Fisher method say about a hour (in a healthy well tuned motor) over 175 F will dry it to under 800 ppm. Low enough to not be much of a factor. Motors with weak rings will take longer and the colder the air temperature the longer it takes.   On a cold motor there is also the condensation temperature. Blowby gases that contain moisture are subject to that cold cylinder wall, like sweat on a glass of ice tea. But also subject to the Law of Partial Pressures. Wear studies by GM and the DOD  indicate wear is a real issue below 85 F and a concern to 140 F but doesn't become a minimal factor until about 160 F. You know this intuitively when you see water vapor exit the exhaust pipe until the system gets above the dew point. It isn't magic, it's physics and it fascinates me. I know you didn't ask but....I over share sometimes. 😉    You keep the Camaro's high and tight.  
    • asilverblazer
      Slate Electric Truck

      By asilverblazer · Posted

      Move further away.   Benefit of living out - none of our cars get short cycled, plenty of warm up time.   Curious how much time/temperature it takes to drive moisture/condensation out of the engine?
    • diyer2
      Transmission Temperature Hitting 220s

      By diyer2 · Posted

      Switch a a 100% synthetic trans fluid, Amsoil works for me.
    • DustMcGrath
      Transmission Temperature Hitting 220s

      By DustMcGrath · Posted

      First of all sorry, I know there are a ton of transmission temperature threads...   My truck is a 2025 LZ0 High (10l89 10-speed) High Country with NHT max trailering package. The NHT package is supposed to have "enhanced cooling."   Normally the trans temp sits around 200. It seems like with any real stress it quickly jumps into the 220s (for example climbing a grade unloaded at lower speeds). I haven't towed much with this truck, but I'm concerned if it gets this hot unloaded.    I've tried a few different things to keep the temps down (tow/haul mode, sport mode, low range when that makes sense) and nothing seems to affect it.    I'm curious if others are the same behavior or if anyone has found techniques to keep the temps down. It seems like it just can't handle reduced airflow at lower speeds, even with relatively light loading.    Thanks!      

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...