• Welcome to the Contour Enthusiasts Group, the best resource for the Ford Contour and Mercury Mystique.

    You can register to join the community.

Can MIL eliminators go bad?

Redlineracer12

Addicted CEG'er
Joined
Apr 26, 2004
Messages
5,538
Location
Twin Cities, MN
I'm not sure if I should put this in here or in the troubleshooting section but I'll just post it and it can be moved if necessary :eek:

I've had the MIL eliminators from MSDS for a few years now and I've never really needed them on the Contour (always had tunes that just turned the rear O2 sensors off) But with my stock tune I'd always get a check engine light. I swapped them over to my cougar now and I am still getting a check engine light. I got a P0161 Downstream Heated Oxygen Sensor Heater circuit fault - Bank No. 2. So maybe the MIL on that sensor is no good? Would there be an easy way to test this? Since the check engine light is on anyhow I'll probably just pull it out and take a look at it. I guess I could cut it open and make sure all the wires are still intact? Or would it be easier to just test and see if I had the right resistance going through it? Maybe this is something completely unrelated but I find it hard to believe I had bad O2 sensors on both cars after removing precats :laugh:

Thanks for any ideas in advance.
 
Yes, they can go bad. Especially if they encounter a lot of heat or anything. It's just basic electronics but you can always have failures.
 
The MIL eliminators have nothing to do with the heater circuit when properly installed.

Either they were installed incorrectly or you have other heater circuit issues.

If yours have a passthrough lug/wiring for the heater circuit, you may have a failed connection or wire in the device. If spliced into an existing O2 sensor harness, I'd suspect they were attached to the wrong wires.

Steve
 
The MIL eliminators have nothing to do with the heater circuit when properly installed.

Either they were installed incorrectly or you have other heater circuit issues.

If yours have a passthrough lug/wiring for the heater circuit, you may have a failed connection or wire in the device. If spliced into an existing O2 sensor harness, I'd suspect they were attached to the wrong wires.

Steve

I don't know how you could install these incorrectly. These are the ones where you just plug them in. Has the male 02 plug on one end and the female on the other. Pretty straight forward for installing. I'll pull that one out of there and try seeing what it looks like inside. I think its just shrink tubing that wraps around it.
 
I don't know how you could install these incorrectly. These are the ones where you just plug them in. Has the male 02 plug on one end and the female on the other. Pretty straight forward for installing. I'll pull that one out of there and try seeing what it looks like inside. I think its just shrink tubing that wraps around it.

Maybe they reversed the wires when they made them.
 
Alright I pulled this bad boy out of the car and cut the shrink tubing open. Unfortunately it's not the type with the board in there so I can't visually inspect much (all four wires collect inside a blue collar and come out the other side) Is there a way I can test the resistance through each of the four? Otherwise I guess I can always re-shrink tube this guy and swap it front to back. Then if I get the code for the front bank I could be sure this was the source. Any thoughts?
 
Okay, looking at it more I tested for continuity through all four wires, 3 of conduct all the way through, one does not :(

Anyone thing MSDS will sell me one eliminator or would I just be better off making my own?
 
The front bank, not the upper sensors. Don't mean to cause confusion.


Makes more sense this way. Yeah, swap it with the other bank and see if you now get a P0141 code.

You should have continuity for the two heater circuit pass-thru wires. The signal-return line should also be a pass-throu.

The signal line should have a high resistance straight thru, usually around 1 megohm or so.

The heater in the sensor should have a low resistance. I forget the actual value and don't have the specs at hand, but I'd expect less that 100 ohms.

Steve
 
You said you had a heater fault code. The detector circuit (ECU) measures current flowing through the heater to determine when one opens (elecrical term), and stops heating the O2 sensor.

There is a fuse for heater current. Check first cause it's your clean job.

The MIL eliminator does nothing to the heater circuit to fool the computer.

As others mentioned, measure the the O2 sensor between the heater pins. It draws several amps, so the resistance will be less than 6 ohms. Zero the meter, and use the R times 1 range to see if the heater is bad in the O2 sensor. If good, go to next.

The next place to measure that same value is at the MIL eliminator where it plugs to the engine harness. After that, you'll need to unplug at the ECU and test from there towards the O2 sensor.

If there's indication that you have continuity from the ECU down to the sensor, through the heater, and back up to the ECU, then the current sensing circuit within the ECU has gone bad, OR, the wiring from the fuse to the ECU is open.

Since I'm a nerd... Inside the ECU is either a series pass resistor over which a voltage drop occurs that must exceed a threashold to say there's heater current flowing, or maybe a hall effect sensor next the the heater conductor measuring current flow above a threashold saying the same. However it's measured doesn't matter. It's either not there due to no heater current, or the measuring circuitry is bad. You can independantly measure the heater current to conclusively determin if the ECU is bad. Do the easier tests I described, let me know, and I will guide you using an ampmeter for the final diagnosis.

Gar
Tony2005 is a great resource
 
I wasn't really all that worried about it since they'll be turned off next week anyhow ;)

I was just curious for the time being. I could always test the O2 sensor out of curiosity though...
 
I agree with ProjectSHO89 and ModernDino. Getting a code for a heater malfunction is not an indicator of a failed MIL eliminator. The MIL eliminator intercepts the voltage signal from the O2 sensor, but does not entirely replace the sensor, as you know. Since the O2 sensor only operates above a particular temperature, the PCM monitors the heater circuit of the sensor. If the voltage goes out of spec, the PCM throws a code. There are two fixes for this. First, you could buy somebody's used O2 sensor. If you're using the MIL eliminator with it, all you care about is whether the heater circuit works. Your second option is to replace the heater circuit with two 10 Watt 10 Ohm resistors in series so that the PCM gets the voltage it expects. The first option is cleaner and will more likely pass a visual inspection during an emissions test.
 
Back
Top