# O2 sensor light reset??? '84 GTI



## JDEcho (Feb 16, 2009)

I just replaced the O2 sensor in my '84 GTI. How do I get the light to shut off? I was told there is a button off the tranny where the speedo cable goes in but I haven't found it. I HAVE ordered the Bentley, just hasn't arrived yet. Thanks, Joe


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## Fat Rabbit (Nov 18, 2001)

*Re: O2 sensor light reset??? '84 GTI (JDEcho)*

There should be a black box under the hood -- follow the speedometer cable from the transmission to the black box. It is hard to see but should be near the area where the coil mounts to the firewall. There is a somewhat hidden button on the box that is pushed in to reset it. IIRC the end of the button was white and down in a tube. I used a Phillips screwdriver to reach into the tube abd to reset it. 
The box is a mileage counter for the recommended O2 sensor service interval -- which, I think, was 30,000 miles back in those days. The box has nothing to do with your O2 sensor actually being bad. Having said that, it is good to replace the sensor on a scheduled basis for good running and fuel economy. FR 
Just noticed it"s Joe from Savage MN. 
One additional thought: If you absolutely can't find the 3" X 2" X1.5" little black box it is possible that someone replaced the speedometer cables with just one cable and eliminated the box. In that case the electrical wiring should still be there and maybe that is shorting out. FR 


_Modified by Fat Rabbit at 2:06 PM 3-2-2009_


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## JDEcho (Feb 16, 2009)

*Re: O2 sensor light reset??? '84 GTI (Fat Rabbit)*

Thanks I'll take a look for it. The car seemed to be running very rich and the mileage was poor (20-22mpg). Car also had an erratic idle which is now cured but runs rougher than before on tip in, then clears up after a few seconds on the throttle. Apparently did something to replace it????


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## Fat Rabbit (Nov 18, 2001)

*Re: O2 sensor light reset??? '84 GTI (JDEcho)*

Joe -- what else have you done on the car? Spark Plugs, SP Wires, Dist Cap, Rotor? It does sound like it needed a new O2 sensor -- 22mpg is not too good. Mine have always been around 31-32 on the highway and a few less in the city. Do I recall correctly that the car sat for a few years? FR


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## JDEcho (Feb 16, 2009)

*Re: O2 sensor light reset??? '84 GTI (Fat Rabbit)*

The car sat for at least 2 years. We put a new fuel line in it and cleaned the ground at the pump to get it running. I soaked injectors 1-3 in seafoam which seemed to help and have added fresh gas and injector cleaner. Set the timing to stock and put new(er) plugs, wires, rotor in it from my brothers newer GTI. At first it was running very weak it never really revved freely until I cleaned the injectors. Then it would run strong and smooth only after it cleared itself out for a second or two(seemed to be rich). Now it takes longer to clear out but it has a consistent idle. It almost seems electrical the way the car goes from rough to smooth, like you hit a switch and voila.... it's all good. It's definitely trying my patience! But man is that little car fun to drive when it's running right!. Of course I'm at a loss. My '66 Mustang is much easier to diagnose and I have a programmer for my truck that reads codes. This little bugger is tough to figure out.


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## JDEcho (Feb 16, 2009)

*Re: O2 sensor light reset??? '84 GTI (JDEcho)*

A little more info on the car. It has 151K on it and my Dad had purchased the car 2-3 years ago for he and my brother to strip it down into a race car. My brother has a '98 GTI 2liter with a 16 valve head, supercharger etc......... they wanted a non-street car. Anyways its old ugly and rusty. It did run when they bought it but then sat and didn't run 2 months ago. They had mentioned getting rid of the car so I asked if they'd help get it running for a commuter car for me. Here we are with a rusty car that barely runs, needs brakes, gas tank, headliner, radio etc.......... Previous owner said the car has a hotter cam in it and header. The header is a 4 into 2 into 1 setup. She's a beast but she's mine at least until I give up on her.


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## JDEcho (Feb 16, 2009)

*Re: O2 sensor light reset??? '84 GTI (JDEcho)*

Is the black box on the inside of the car or under the hood?


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## motorbreath1800 (Jan 11, 2008)

Right above the brake booster, it's a small 4" black box with a white button on it. Push the button in while the car is running.


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## WackyWabbitRacer (Apr 24, 2001)

*Re: (motorbreath1800)*


_Quote, originally posted by *motorbreath1800* »_Right above the brake booster, it's a small 4" black box with a white button on it. Push the button in while the car is running. 

That is true for the earlier MK1 cars.
On the 1981 and later MK1 cars, the oxygen sensor reset is on the left side of the instrument cluster. The instrument cluster bezel must be removed to access both the EGR and the Oxygen Sensor resets.
After removing the bezel, use a coat hanger wire about 6 inches long with a small hook formed at one end. 
Use the wire and insert the hooked end into the opening at the left top of the cluster. Pull the right hand lever for the oxygen sensor reset toward you. 
Cheers, WWR.


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## JDEcho (Feb 16, 2009)

*Re: (WackyWabbitRacer)*

Thanks WWR. I was able to use my newly purchased injector o-ring remover to perform that task! Always feels good to use a new tool more than once. So yes the light is off. On to the next project on the list...........


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## stick90 (Feb 28, 2008)

*Re: (JDEcho)*

Just ignore the light.


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## kamzcab86 (Feb 14, 2002)

*Re: (WackyWabbitRacer)*


_Quote, originally posted by *WackyWabbitRacer* »_
That is true for the earlier MK1 cars.
On the 1981 and later MK1 cars, the oxygen sensor reset is on the left side of the instrument cluster. 

Not true for the Cabriolets. All 1981-1987 Cabriolets use the OXS counter box mounted to the firewall, which is where the reset button is on those cars.
The thread is about an '84 GTI and the instructions for it are accurate; just wanted to correct WWR's posted info.










_Modified by kamzcab86 at 6:32 PM 3-3-2009_


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## WackyWabbitRacer (Apr 24, 2001)

*Re: (kamzcab86)*


_Quote, originally posted by *kamzcab86* »_ All 1981-1987 Cabriolets use the OXS counter box mounted to the firewall, which is where the reset button is on those cars.


Thanks for the correction on the Cabby's.
Cheers, WWR.


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