[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!

 

[Buster28]

The IAT sensor has two wires, one is ground the other is referenced to +5 Vdc

 

[Kuenjchen]

You just measured the connector with ignition on and no sensor, the voltage should be 5v? I got 12v. Can I share other sensor’s 5v? Or install a 5v regulator?

 

[Buster28]

If the Ignition Switch is Off there should be no voltage on either IAT wire and +5 Vdc on the Yellow/Green when the Switch is On.
If you read +12 Vdc it is wired incorrectly, the +5 Vdc source is inside the Powertrain Control Module (PCM).

 

[Kuenjchen]

I didn’t wire it! It just happened one day suddenly!

 

[Buster28]

Where are you connecting the negative side of the voltmeter?

 

[Kuenjchen]

Where are you connecting the negative side of the voltmeter?

Connector, should be grounded?

 

[Buster28]

One of the IAT sensor pins is ground. If you disconnect the connector and measure across the two pins with the Ignition switch in Run the expected voltage is 5 Vdc.
If you measure the IAT sensor resistance at 60 degrees F , the resistance should be about 4500 ohms.

 

[Kuenjchen]

Can I use other sensor’s reference 5v or install a 5v voltage regulator lm7805? Thanks!

 

[Shawn Anthony]

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.

 

[Kuenjchen]

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!

 

[Shawn Anthony]

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.

 

[Kuenjchen]

Adjust C3

Adjust C3? What does it mean and how to do it?

 

[Buster28]

There are two separate +5 Vdc power supplies on the PCM circuit board, they power:
Crankshaft Position Sensor
Accelerator Position Sensor #1
Accelerator Position Sensor #2
Accelerator Position Sensor #3
Throttle Position Sensor #1
Throttle Position Sensor #2
Vapor Pressure Sensor
MAP Sensor
EGR Sensor
IAT sensor
DLC Serial Data
Coolant Temperature Sensor

Since the engine is running and the only DTC is for the IAT Sensor it is not likely there is a PCM +5 Vdc power supply problem.

 

[Buster28]

OK Shawn, this is a 00-02 Trooper PCM, how about identifying the two +5 Vdc power supplies.

 

[Shawn Anthony]

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.

 

[Buster28]

All your technobabble does not help the originator of this post to solve his problem.

 

[Kuenjchen]

One time the alternator was bad and I replaced the alternator. I didn’t wire anything else and it just happened! The connector is floating in the air and it shouldn’t be grounded. It is possible that 5v touched 12v somewhere in the iat wire? So can I just disconnect the iat 5v wire and use other sensor’s 5v?

 

[Shawn Anthony]

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 ..it 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.

 

[Kuenjchen]

No short, replacing the PCM will fix the problem;
If shorted, replacing the PCM won’t fix the problem.
That’s my understanding, right?