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P0112 keeps coming back

774 Views 34 Replies 4 Participants Last post by  Kuenjchen
Isuzu trooper 2000 3.5 L
I have replaced so many iat sensor from web, none of them are working! I’m waiting for oem sensor from Japan.I have replaced the connector too, still no luck. I wonder it’s the wire problem? Which pins shall I use to install a new wire for iat connector? Also I measured the connector with ignition on , I got 12v instead of 5v , what’s wrong with these symptoms? Is it reference 5v grounded problem? Will installing a new wire and disconnecting original iat wire fix the problem ? Your help is appreciated!
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Can I use other sensor’s reference 5v or install a 5v voltage regulator lm7805? Thanks!
If you are getting 12V on the ref+ (yellow/green) wire, this means the ECM internal power supply regulator circuit for Vss-Ref has "gone to the rail" as it's called.

The easiest way to go about returning the voltage back to 5V is to simply repair the ECM Vss-Ref power supply. There is a few different ways the Vss can go to the rails, they are;

1, the voltage diver that adjust Vout is pulling Vset low. This would make the IC output maximum potential that is equal to Vbb+

2, The capacitor C2 is shorted across Vin & Vout pins of the IC which is providing a DC current path around the regulator circuit. Again causing Vout to equal Vbb+

3, the regulator IC is shorted to Vin & Vout.

4, If the regulator is a TO-220 case device the insulator between the case and the heat sink is leaking current. Causing the IC to put maximum potential also equal to Vbb+.

If you have a LM7805 laying around you can simply drop that into the ECM 5Vref supply. Afterwards you will need to adjust C3 to bypass filter the alternator ripple.

If all sounds to complicated, I have remanufactured ECMs in stock available.
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Replacing ECM might cause other problems?
I’ll try lm7805 first, ECM last resort ! What’s the ECM’s price? Thank you for your help!
Isuzu ROM pramiters are all the same. Like for like there is nothing prevent the replacement of a faulty unit. I'll PM you my number, when you are ready to purchase feel free to give me a call.
OK Shawn, this is a 00-02 Trooper PCM, how about identifying the two +5 Vdc power supplies.
Near the thermistor.

Your turn...
In this very basic circuit described the current flow of error amp1 while the load is pulling the supply towards negative in relation to the ref voltage. Bonus points calculate the current divider circuit values by assuming
It = 50ma & Et = 143v.

Rectangle Font Line Parallel Pattern
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All your technobabble does not help the originator of this post to solve his problem.
The stone cold defection of your response was a very creative & polite way of portraying to dish & not take. No worries, it's cool as it makes no difference to me. What you fail to see is we are on the same team.

My "technobabble" is far from babble accurate information on the process and involvement of what is required to install a replacement regulator. Most importantly it clearly paints a picture that the process of installing a 65 cent LM7805 IC is far far far beyond what was first imagined. Perhaps the OP is now thinking that's not the best way to go about it. And just maybe that person will be more inclined to listen to your or my sound sound advise. Maybe send out a suspected ECM to be repaired..who knows.

With that said:
V2 is the error amp, current flow leads out from the cathode of V1 and on into the output of the Vss+ supply. Carry on with the good deeds my good man.
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