I'm looking for a way to have my Check Engine light come on for 5 seconds and then shut off when I start the car. Excluding having an ECM. I will of course be doing this for emissions reasons. I'm working on getting rid of the ECM but I need some way to make the light come on at startup because I'm going to replace the distributor and carb. I'm able to solder and just need to know what parts I need to get to create something to hook this all up.

Thanks,
Matt

[This message has been edited by Golden80 (edited April 17, 2001).]

[This message has been edited by Golden80 (edited April 17, 2001).]

 

Golden,

Sorry, I'm not an "electronic" engineer, only an electrical engineer.

You can easily install a timer that would operate a relay to drive the MIL lamp. Remember that the lamp has a 12VDC source all the time, and the ECM only completes the ground path for the lamp.

You can accomplish your goal by either a timer, or have the lamp remain on whenever the ignition is ON but the engine is not running (just like it would with an ECM). The easy way to operate the ground circiut of the light in this way is with an oil pressure switch - the type used to operate an "idiot" light instead of the fuel pump or a gauge. The oil light switch simply grounds the circuit for the lamp, just like the MIL lamp would require. There would be no timer and other components. The light would actually be functional then, but only you would know that the "Check Engine" would mean "Check Engine Oil".

You could also install a timer as you suggested, but the circuit would be more complicated, and you would eventually spend more money than a simply oil pressure switch and a piece of wire would cost. You could build an IC timer circuit with a 555 and output transistor to drive the relay, but the relay and components alone would cost about $15.00. Commercially available cube type interval timers, available for about $20.00, would be suitable except for that most are made for either 24VAC or 120VAC power, not 12VDC. An oil pressure switch from WrenchHead.com is $10.57 - you make the call.

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Later,
Vader
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[This message has been edited by Vader (edited April 17, 2001).]

 

Something like this should do just what you want:



Since the ground connection for the MIL lamp is already wired to terminal 'D' of the ALDL connector, just wire one leg of the oil pressure switch to that point and the other leg of the switch to ground.

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Later,
Vader
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"What a Day..."
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[This message has been edited by Vader (edited April 17, 2001).]

 

VAder, the problem with your circuit is it will stay on constantly with OP, not exactly what he's looking for. You need a simple timer circuit, offhand i can't remember if a 555 timer could support a bulb or not.
Somebody will probably jump in before i get home to check this out.
...ed

 

Vader.. i have a quick related question, using the ALDL connector since it has an input for the shift indicator light, can I wire the shift light to go on when a switch (like a window switch) is on? I hate the stupid light, and want to use it for something good.

I was figuring, if it works like the oil light, that I could just wire a 12V "on" signal from the switch to the number on the aldl corresponding to the shift light.. but I am assuming the light would still come on also when it normally supposed to.. could I cut the wire that goes into the ALDL at the shift light terminal (assuming that comes from the ecm when it wants the light to go on) and make the light stop coming on when the ecm thinks i should shift.

Thanks for any help.

 

Here's a simple circuit that will illuminate the check engine light for approximately 5 seconds at ignition power on, and would cost less than $3 to build. (Radio Shack part numbers are listed on the schematic). The circuit uses two bipolar NPNs in a Darlington configuration, to reduce the base current required for saturation, with an RC supplying the current to the base, until the cap is charged. A second resistor discharges the cap through the system load at power down.

A 555 could be used for the one shot function, but it would have to drive a transistor to control the light bulb, since a 555 will only sink 200 ma (100 ma for a 555C), and the check engine light bulb draws on the order of 250 ma.

Tim

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You can use a standard automotive relay if you want to stay with Vaders oil pressure switch idea......

 

I'm assuming the oil pressure switch will ground with NO oil pressure (in other words, normally grounded), and open when oil pressure is present.

In which case his circuit will work perfectly.

It's absolutely no different than the way the ECM turns on the light.

Now if the OP switch grounds with pressure and opens with no pressure, you're going to need a relay to fix that little problem.

 

Ed,

Actually, most of the older GM and Ford "idiot light" oil pressure switches are NC, not NO. Once pressure is maintained (usually about 4-7 PSIG) the light will no longer be grounded.

A 555 is good for about 150mW output IIRC, but not for long. Aside from that, a decent smog inspector will recognize the timer for what it is almost immediately, since a "real" SES lamp stays on until the engine is running.

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Later,
Vader
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"What a Day..."
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