How To Install An O2 Sensor Simulator
By Matt Beazer
Last Updated 6/06/05
Last Updated 6/06/05
WARNING: This DOES NOT work!
It ran fine for a couple weeks, then spit out the code 21 again. I'm investigating future fixes, but it looks like you will have to wire the O2 sensor inline for the heater function. From what I've found out, on some cars the PCM seems to need to see the load of the O2 sensor heater, otherwise you'll get a code. More when I decide to fiddle with the wiring some more. Note that it does stay off for a while, then come on, then blinks off again. No big deal, but it's annoying. I've left this up as a general guide to installation, but if you want to avoid the code 21, you'll want to wire in the O2 sensor heater as it shows in the instructions included with the O2 simulator.DISCLAIMER:
DO NOT ATTEMPT THIS MODIFICATION IF YOU DO NOT HAVE THE
TECHNICAL EXPERTISE TO DO
SO SAFELY.
WE TAKE NO RESPONSIBILITY FOR THE RESULTS OF THIS MODIFICATION.
Introduction
All OBD-2 cars come with at least two O2 sensors, one before and after the cat. They may come with as many as four, as V6, V8, V10, etc. cars have two banks of cylinders, and each bank may have it's own catalytic convertor. The O2 sensor after the cat is used only to monitor the health of the cat. If it detects a loss of efficiency in that catalytic convertor, it triggers a code, lighting up the check engine light.
This is a pain in the rear for a number of reasons, one being the extra cost if you're replacing them on the 100,000 mile replacement schedule and you end up having to buy two O2 sensors instead of four. The after-cat O2 sensor also tends to be more expensive due to the extra length of the wiring needed, plus the second O2 sensor is designed to be better shielded against water contamination. This is because water is a natural byproduct of the catalyst. Other reasons include not wanting a catalytic convertor for off-road use, or if you're installing a header and don't want to deal with the hassles of the second sensor. I chose to remove the second O2 sensor because I was planning on playing with welding up a 2.5" downpipe for my Neon, and didn't want to deal with welding in the O2 sensor bung just for the worthless second sensor.
I chose to use the product sold at www.o2simulator.com because of it's simplicity, cheapness, and effectiveness. It runs $30 shipped when many are running in the $80+ range. It also allows full removal of the second O2 sensor, while others just prevent the ECU from detecting the lack of the catalytic convertor. The support is also excellent, which helped me get over a hurdle on the way to getting it to work on my 1998 Neon. Here's a picture of what it looks like:
It's a simple small brick of epoxy, surrounding the circuit board and a green LED. The LED is bright enough to show through the epoxy. It's simple and waterproof, but won't make your friend ooh and ahhh about it. If you don't like it, dip it in some yellow paint, since you know yellow is a "fast" color. You'll probably gain 20+ HP too! It looks bigger here than it is, it's only 1"x.25"x.25", so it doesn't take up much room.
Installation
Tools needed:- Wire snips
- Soldering Iron
- Solder
- Electrical tape or preferably heat shrink tubing
- Zip/Cable Ties
First, disconnect the negative battery terminal and jack the car up. Just one side is fine, just get it high up in the air enough to get at the second O2 sensor, which is mounted right after the catalytic convertor. It sits in a little crimp-bent section of the exhaust, which in my opinion is the biggest cork in the stock exhaust system besides the cat. Pull back the rubberized shielding on the wiring, leaving at least 6" of wire attached to the O2 sensor. This way you get a "free" replacement O2 sensor if the upstream sensor ever goes bad. I zip-tied the wires up out of the way so they'd not drag on the ground. Alternately you can grab an o2 sensor connector off a boneyard Neon and not have to hack the wiring up of the second sensor at all, just zip-tie it out of the way.
Climb out from under the car, and reach down to the passenger side of the exhaust manifold (hopefully it's not hot). I hope you have a cold-air intake like the Iceman, otherwise you're going to likely have to remove the airbox to get at it. There's a pigtail there for the O2 sensor hookup, grab it and pull the now-cut wires up from under the car, then undo the connector. It's a simple plastic tab you pull up on before pulling apart the connector. Don't snap off the retaining tab by accident. Take the connector and it's wiring to a clean work area so you can lay it all out easily in good light. I'd not recommend doing this while it's still plugged into the car, it makes it harder than it needs to be. I think the pinout is the same for all of the OBD-2 Mopars, but I don't know for sure. If you're doing this on a non-Neon you'll want to pull the loose end of the wires up while leaving the connector plugged in, then use a multimeter to verify what wires are the power, ground and signal wires. Note that the instructions say you should get 12v with the key in the "on" position, but on my Neon the car had to actually be running for voltage to show up on the multimeter.
If your O2 sensor is a stock one, you should have four wires coming out of the O2 sensor plug, one black, one gray, and two white. The black is the O2 sensor signal to the ECU, the gray is the O2 sensor signal ground, and the white wires are the O2 sensor heater +12v and ground wires. If you have an aftermarket sensor, the colors may vary slightly, but the pinout will be the same. Here's a picture to illustrate.
(Click For Larger Image)
Ignore the solder joint on the heater
ground, that was due to my own addiction of more wire to the plug after
I snipped it thinking I'd not need it. Oops. Keep this
layout in mind, you don't want to run +12v to a ground by accident!
First, strip a bit of insulation off each wire on both the O2 simulator and the wiring pigtail. Then you need to solder the wires together as shown in this image:
(Click For Larger Image)
I chose to use some velcro and stick it to the passenger side strut tower so I can monitor it easily and know it's not in the way of any moving or hot parts. It doesn't need to be in plain sight, you can hide it if you want. That way it's out of the sight of those prying inspectors if you live in a smog-Nazi socialist country, er, state, like California.
(Click For Larger Image)
Overall installation is simple, once you know the tricks on installing it on a Neon. Initially I had problems with a persistant code 21 being kicked out by the ECU, which is an O2 sensor problem; in this case, "P0137, "Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 2)" according to my OBD-2 scanner. The support rep at www.o2simulator.com expressed the opinion that this was due to the simulator not getting the full 12 volts, likely due to the ground for the heater not being hooked up. The instructions were designed around people bypassing the O2 sensor but leaving it in place in the harness, not removing it completely like I did. This is why you have to hook both ground wires from the O2 sensor plug to the simulator. After soldering the two grounds together to the ground on the simulator I've had no problems with this code after resetting the ECU by disconnecting the battery. Next step is just fabricating the 2.5" downpipe to match the rest of my exhaust system.
First, strip a bit of insulation off each wire on both the O2 simulator and the wiring pigtail. Then you need to solder the wires together as shown in this image:
(Click For Larger Image)
The white +12v heater power wire goes to
the red wire on the O2 simulator. The black signal wire hooks to
the white O2 simulator wire. BOTH of
the ground wires, for the heater and for the O2 sensor signal, connect
to the black ground wire on the O2 simulator. If you don't
connect both ground wires to the O2 simulator, the ECU will trip a
trouble code and your check engine light will glow intermittently at
you in an annoying fashion.
Solder all connections by twisting them together in the middle, then heating the wires using the soldering iron tip until the solder melts on the wire, making a solid connection. If you're using heat shrink tube (which I'd prefer, but didn't have handy), make sure you slide it over the wires before soldering them. Otherwise just wrap in electrical tape like I did here. Don't half-ass it and not solder the wires, you'll regret it in the future.
When done, plug it back into the O2 sensor plug in the car, reconnect the battery, and start it up. I'd not wrap up the wires yet, you'll want to test-drive it for a couple days first to make sure no codes pop up. They shouldn't if you wired it right. Zip-tie the wires out of the way of the exhaust manifold and moving parts, though!
It will stumble as it re-learns the crank/cam positions, and you'll hear an odd buzzing noise as the idle control motor whirs as the computer learns it's positioning, then it'll start fine on the second crank. Take it for a test drive and check for codes, you shouldn't get more than a code 12 (battery disconnected within the last 50 crank attempts) and 55 (listing done). While the engine is running, check for the glowing green LED inside the epoxy brick. It should blink slowly, once every couple seconds. This means it's working correctly. If it's not blinking at all, you don't have 12v running to it. If it's blinking rapidly, this indicates the simulator isn't getting the full 12 volts it should be getting, and you need to check your grounds and other wiring. Here's a picture of it glowing:
(Click For Larger Image)
Drive it for at least 50 miles, preferably stopping from time to time with the engine off while you run into a store, etc. You shouldn't get any codes; if you do, check your wiring. After 50 miles or so the ECU will have completed all of it's emissions/engine tests, including the O2 sensor tests. At this point feel free to wrap the wiring up in something to protect it, I used electrical tape, though you could use convolute tubing for an easier to remove solution in case of wiring troubles. It should look something like this:
Solder all connections by twisting them together in the middle, then heating the wires using the soldering iron tip until the solder melts on the wire, making a solid connection. If you're using heat shrink tube (which I'd prefer, but didn't have handy), make sure you slide it over the wires before soldering them. Otherwise just wrap in electrical tape like I did here. Don't half-ass it and not solder the wires, you'll regret it in the future.
When done, plug it back into the O2 sensor plug in the car, reconnect the battery, and start it up. I'd not wrap up the wires yet, you'll want to test-drive it for a couple days first to make sure no codes pop up. They shouldn't if you wired it right. Zip-tie the wires out of the way of the exhaust manifold and moving parts, though!
It will stumble as it re-learns the crank/cam positions, and you'll hear an odd buzzing noise as the idle control motor whirs as the computer learns it's positioning, then it'll start fine on the second crank. Take it for a test drive and check for codes, you shouldn't get more than a code 12 (battery disconnected within the last 50 crank attempts) and 55 (listing done). While the engine is running, check for the glowing green LED inside the epoxy brick. It should blink slowly, once every couple seconds. This means it's working correctly. If it's not blinking at all, you don't have 12v running to it. If it's blinking rapidly, this indicates the simulator isn't getting the full 12 volts it should be getting, and you need to check your grounds and other wiring. Here's a picture of it glowing:
(Click For Larger Image)
Drive it for at least 50 miles, preferably stopping from time to time with the engine off while you run into a store, etc. You shouldn't get any codes; if you do, check your wiring. After 50 miles or so the ECU will have completed all of it's emissions/engine tests, including the O2 sensor tests. At this point feel free to wrap the wiring up in something to protect it, I used electrical tape, though you could use convolute tubing for an easier to remove solution in case of wiring troubles. It should look something like this:
(Click For Larger Image)
I chose to use some velcro and stick it to the passenger side strut tower so I can monitor it easily and know it's not in the way of any moving or hot parts. It doesn't need to be in plain sight, you can hide it if you want. That way it's out of the sight of those prying inspectors if you live in a smog-Nazi socialist country, er, state, like California.
(Click For Larger Image)
Overall installation is simple, once you know the tricks on installing it on a Neon. Initially I had problems with a persistant code 21 being kicked out by the ECU, which is an O2 sensor problem; in this case, "P0137, "Oxygen Sensor Circuit Low Voltage (Bank 1 Sensor 2)" according to my OBD-2 scanner. The support rep at www.o2simulator.com expressed the opinion that this was due to the simulator not getting the full 12 volts, likely due to the ground for the heater not being hooked up. The instructions were designed around people bypassing the O2 sensor but leaving it in place in the harness, not removing it completely like I did. This is why you have to hook both ground wires from the O2 sensor plug to the simulator. After soldering the two grounds together to the ground on the simulator I've had no problems with this code after resetting the ECU by disconnecting the battery. Next step is just fabricating the 2.5" downpipe to match the rest of my exhaust system.
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Questions? Comments? 