Dumb question regarding 'ENGINE' light.....

Discussion in '6.9L IH & 7.3L IDI Diesels' started by whiteboyslo, Dec 26, 2013.

  1. whiteboyslo

    whiteboyslo FNG

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    Which sensors/conditions activate the ENGINE light? I know oil pressure is one since I just installed an aftermarket gauge using the location of the OEM sending unit for the aftermarket one (OEM is disconnected for now). Just wondering what else would trip this light for future reference.

    Mike

    PS - Couldn't fit a T at the location the Banks turbo uses for the sensor relocation (at the turbo), so my plan is to move the aftermarket sending unit to the port on/near the oil cooler at the next oil change.
     
  2. cpdenton

    cpdenton Truck needs paint. Supporting Member

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    I am interested in changing my aftermarket sender to this lower location as well. I have looked and can't find exactly where it is. Post a picture once you get it done.

    I was able to work a t in the location that banks provides, but I do not like it.

    Then I will have the aftermarket gauge measuring the lower end oiling, and the factory idiot light making sure the turbo is oiled.
     
  3. jonathan

    jonathan Full Access Member

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    On the drivers side head at the front there is a over heat sensor that will cause the dummy light to come one iirc it activates at 242 degrees
     
  4. icanfixall

    icanfixall Official GMM hand model

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    I do believe the low oil pressure and coolant temp is all thats connected to this "engine lite. Many times the reason it comes on is the oil pressure sender electrical connection is loose. Just crimping it with some pliers will fix that. Also sometimes the over temp switch goes bad and causes the lit to come on. It also causes the temp gauge on the dash to peg way over past the "L" on normal.. To test this switch remove the wire and ground the end of it. No matter how warm or cold the engine coolant is the dash gauge will peg over..
     
  5. whiteboyslo

    whiteboyslo FNG

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    I thought it activated a separate light on the right of the steering wheel.....

    Mike
     
  6. icanfixall

    icanfixall Official GMM hand model

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    You might be correct about that lit lite to the right of the wheel. I recall something about check engine in red telling me too late bud... Been a long time since I saw that lite. Need to go check and see...
     
  7. LCAM-01XA

    LCAM-01XA Full Access Member

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    The engine light is activated by the overheat switch closing at approximately 247F and grounding the signal wire for the temperature gauge. The actual sender for said gauge swings between 74 ohm when engine is cold and 9.7 ohms when engine is hot. Basically the hotter the engine gets the lower the resistance in the signal wire and the higher the gauge reads, when the overheat switch kicks in the resistance in the signal wire drops to nothing and thus the gauge starts reading as high as it can get.

    The gauge itself does not trigger the actual red "engine" light, and neither does the overheat switch. The light's operation is handled entirely by a little circuit board called "engine warning indicator module", it monitors resistance in both the temperature gauge signal wire and the oil pressure gauge signal wire. Why said module is needed, well cause a simple light bulb can't respond to two opposite signal patterns, and oil pressure gauge apparently works exactly the opposite of the temperature gauge - the switch for it is open when there is no oil pressure and closes and grounds the signal wire during normal operating conditions. In other words the lower the pressure the higher the resistance, and the higher the pressure the lower the resistance - and if you were to unplug the switch wire altogether that would read as infinite resistance and suggest no oil pressure, say hello to a brightly-lit red "engine" light.

    In case anyone is wondering, the warning module can be removed without adversely affecting either gauge's operation - this is because it doesn't intercept the gauges' signals, but rather it piggybacks to them, in other words the warning module is wired in parallel with both the coolant temperature gauge and oil pressure gauge. If you were to remove the module the temp gauge will still peg up when engine overheats and oil pressure gauge will still peg down when pressure drops way too low, you just won't have the red "engine" light coming on.

    Another important note, the module will work properly even if you've ditched the factory pressure switch and are now running a sender with the gauge circuit board resistor jumped (or alternatively, in case of bricks, you've switched to a complete '87 gauge cluster).
     
  8. jonathan

    jonathan Full Access Member

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    Thanks for clearing that up lcam
     
  9. Agnem

    Agnem Using the Force! Staff Member Supporting Member

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    Excellent response to that question!
     
  10. 89Laredo

    89Laredo Underemployed

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    I didn't know there was an engine light... Some jackass tore my dash apart before I bought the truck and I don't have the indicator lenses anymore.
    Unless you mean this engine temp one...
    [​IMG]
     
  11. LCAM-01XA

    LCAM-01XA Full Access Member

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    89Laredo, I don't know what your truck has, as I do not have an '83-'86 EVTM. I have one for '87-'91, a lot of the information inside it applies to '92-'94 IDIs as well, but the '83-'86 IDIs tend to be a breed of their own. For example the '87-'91 have a light that doubles as a warning for both too high engine temp and too low oil pressure, whereas you already found your overheat light and you probably have a separate low oil pressure light somewhere else. Your oil pressure gauge also reflects real oil pressure, whereas everything '89-up (and possibly '88 too) has the gauge twisted into nothing more than an idiot light with a needle - it can be made properly operational, but yours already is from the factory, thus maybe no need for low oil pressure light? Idk, but the OP's truck is a '91 so I was able to answer his question. What you're working with is somewhat different, there's a good chance very little of what I posted can be useful to you.
     
  12. 89Laredo

    89Laredo Underemployed

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    Ahh. I'm on tapatalk and didn't see a year mentioned, just assumed it was an older truck.
     
  13. LCAM-01XA

    LCAM-01XA Full Access Member

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    It's in his signature, probably why you didn't see it. But no, it wasn't explicitly mentioned in any post, sorry about that.
     
  14. whiteboyslo

    whiteboyslo FNG

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    To be honest, I haven't seen the other port......yet. I just remember reading about it when I was researching methods to hook up the gauge.

    I finally did manage to get both sensors hooked up. It took a lot of trial and error to get everything in and to figure out the install sequence so everything would fit. I eventually had to temporarily remove the intake hat to make it all work. I couldn't drive around with the ENGINE light on all the time, though. It would've driven me nuts!

    LCAM, can you be a bit more specific in your response? (Kidding) Thanks for the info!

    Mike
     
  15. LCAM-01XA

    LCAM-01XA Full Access Member

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    The other oil pressure port is right between your exhaust pipe and your transmission slave cylinder, the plug doesn't stick out too much but if you can't see it just run your finger along the side of block there and you'll feel it. I'll see if I can get a decent pic, I got a braided line hooked into it which makes it very hard to miss LOL
     

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