Code 172
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Code 172
I have had intermittent CE lights for the last couple of days on a 93 Bronco XLT with a 302 an dauto trans. I checked the codes and came up with a 172 HEGO (HO2S) senor fail/ lean. What does this mean? Is it a bad O2 sensor or am I running lean? Any help would be appreciated!
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I've had that one... It's either fixed with a new O2 sensor or new EGR valve. If you're not getting any EGR codes, I'd start with the O2 sensor. They're not that cheap ($50 if I recall) but only take 3 minutes to replace and they do seem to wear out every few years. I've put a couple in my 1992.
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From: Texas
Could be several things, you could be running lean, possible vacuum leak on that one. It also could be a small exhaust leak before the 02 sensor. The negative pulse between cylinders firing will sometimes suck extra oxygen in and the sensor will pick it up. You could of course, have a bad sensor as well. A misfire could cause that code also because of all that unburned oxygen headed down the exhaust pipe.
Here is one quick way to check if it is lean. With the engine running, squirt some starting fluid down the intake tube, if the engine smoothes out and starts running better, it probably is running lean, you richened it up with the starting fluid. If it runs worse, then you made it too rich, so it was probably running ok before.
Here is one quick way to check if it is lean. With the engine running, squirt some starting fluid down the intake tube, if the engine smoothes out and starts running better, it probably is running lean, you richened it up with the starting fluid. If it runs worse, then you made it too rich, so it was probably running ok before.
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If it helps narrow it down a little, I only get the CE light after it warms up. I drive about 40 miles one way to work and I start getting the CE about half way. As far as that, it looks like it could be the O2 sensor, EGR or maybe exhaust leak. Correct me if I'm wrong but it would seem to me that if it was a misfire or if it were to run lean it would happen sooner. The other twist is if I pull over and kill the engine and then start it back up, the CE light goes out for a few miles and then comes back on.
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From: Cary
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So, as I understand it, I should replace the O2 sensor and see if that takes care of it. If it doesn't it is either the EGR or an exhaust leak.
If this is the case, I will be getting an O2 sensor and the "special" socket first thing Sat morning. I'll let you guys know what happens. Anything I need to be aware of when changing it?
If this is the case, I will be getting an O2 sensor and the "special" socket first thing Sat morning. I'll let you guys know what happens. Anything I need to be aware of when changing it?
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From: Texas
It's better not to change it with exhaust totally cold. The warmer the better as far as getting it out, they are very prone to be rusted or frozen in place and don't like to come out. Drive it first so it's warm.
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This morning I went to fill up the ol' gas tank and the station didn't have any regular so I had to use mid grade. About half way to work the CE light came on once for about 5 seconds and then went out. It didn't come back on again the rest of the drive. To say the least, it through me for a loop. Would the grade of fuel matter to the O2 sensor?
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