2003 Dodge Dakota 4.7 H02 sensor control circuit

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Originally Posted By: clinebarger
If this wasn't a Chrysler product.....I would seriously question a PCM replacement. Even then I would go through the motions of quick testing the heater circuits with a test light at the PCM connector pins. The test light should light on all 4 heater control pins.

(Test Light hooked to B+, All PCM Connectors unplugged)


The last Chrysler I did any real work on was a long time ago but I am surprised they are not protecting the circuit with even a fusible link never mind a fuse.
The part lives in a high heat environment and the wires right near the hottest part of the exhaust, what are they thinking?
 
Since a circuit inside the PCM is sourcing the power for the heaters, it is the circuit protection.

If it is the circuit in the last California diagram, I would disconnect the battery, unplug the PCM, and measure the resistance from the PCM plug to ground through each of the 4 heater circuits. It should be about the same on all, which I think an O2 sensor heater is usually 10-20 ohms. If you find open circuit or short, the sensors and wiring need to be checked out.
 
Originally Posted By: mk378
Since a circuit inside the PCM is sourcing the power for the heaters, it is the circuit protection.


Well yeah okay I should have said additional protection, the PCM is a dam expensive fuse.
 
Originally Posted By: Trav


The last Chrysler I did any real work on was a long time ago but I am surprised they are not protecting the circuit with even a fusible link never mind a fuse.
The part lives in a high heat environment and the wires right near the hottest part of the exhaust, what are they thinking?


I guess they think the driver can be shut down before any damage is done?
 
I have seen this issue before. Check for a p/s fluid leak wicking into the harness. Somewhat common on these , p/s fluid leaks in to the wiring harness.
 
New computer didn’t fix it.

I clear the codes, as soon as I start the truck the three codes come right back.

Separate issue, either the prior owner or the original owner bashed out the MIL and ABS bulbs in the dash. So I need to figure out how to replace those. They aren’t 194’s, they’re tiny bulbs with two metal prongs sticking out of them that almost look like an LED.
 
Are they LEDs? Do they solder in or plug in?

Do the resistance checks of the sensor heater circuits.
 
I think it's an LED. It looks like this, but the poles sticking out are much shorter:



Must be solder in.

I'll check the resistance next, as well as check to see if the PS is leaking onto the harness.
 
Just checked and the pressure sensor for the power steering pump isn't even there. The plug is, but it looks like a repair was made at some point due to a leaky sensor and they just removed it?

Very strange. I'm going to try replacing the o2's and see if that fixes it. I think all 4 are the same sensor since it has the standard trans.
 
You're really going to buy and install four sensors rather than take 15 minutes testing?

It's also clear that this truck's wiring and previous owners' work is suspect.
 
Last edited:
By the way, that power steering sensor is on the same ground as the o2. By that sensor being missing, will that mess up the o2's? I wonder.
 
Originally Posted By: oilpsi2high
By the way, that power steering sensor is on the same ground as the o2. By that sensor being missing, will that mess up the o2's? I wonder.


I would certainly replace the PS sensor before anything else. Did they leave the connector?

Are you sure this truck only has 59k? Awfully low mileage for a 2003, especially since a lot of other things have been tampered with.
 
The connector is there, but there's nowhere to plug the sensor into on the pump. It's like the PS line was replaced and they just said to [censored] with the sensor or something.

I think the mileage is accurate. The truck was owned by a brewery, the interior is brand new, and the pedals have minimal wear as well. I think the guy bought it with the light out, and VT doesn't have emissions testing so they probably had no idea.
 
Originally Posted By: oilpsi2high
The truck was owned by a brewery



beer3.gif
Well that explains everything. How many did they have before working on the truck?
grin2.gif
 
Originally Posted By: JetStar
Originally Posted By: Trav
I have no idea but I remember old OBD I systems burning the drivers on some cars.


I recall that to. Now we have hundreds of smart High side drivers that can not only protect the output, but also provide status of the load.
I first encountered these on some old Boeing 777 avionics. Here is an example of the many available.

http://www.onsemi.com/pub/Collateral/NCV8460-D.PDF



Thanks very much for that! Now I understand a little more about the circuits.
 
Originally Posted By: dishdude
Originally Posted By: oilpsi2high
The truck was owned by a brewery



beer3.gif
Well that explains everything. How many did they have before working on the truck?
grin2.gif



Not as many as I'm going to have when I'm finished working on it!
 
I think @oilpsi2high might be onto something with the PS sensor/shared ground suggestion. It ought to be easy to rule out in any event though.

Found a pretty quick testing procedure online for the 1st DTC listed:

"
...
Check the resistance on the heater circuit to determine if it is over 10A.

Test procedure:

With key on and the engine off, use a voltmeter to check for 12+ volts fused battery feed to the heater element.

If there is no voltage present, repair open or short in the 12 volt feed circuit but first determine if it is necessary to replace any fuse blown from the short.

If the battery feed is correct, remove the ground (control) circuit from the ECM wiring connector and check for resistance on the circuit.

If there is infinite resistance, repair the open in the circuit.

If the resistance is above 10A and the control circuit is good, suspect a bad O2 sensor. Replace the sensor and recheck.
...
"
 
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