EEC codes 157 and 176

[92ShoOff]

Okay so my Check Engine light is back on again and I'm now getting codes 157 (MAF circuit below minimum voltage) and 176 (HEGO sensor indicates system lean [LH]) with my code reader. I had recently taken my whole upper intake manifold off to change my valve cover gaskets, oil well seals, and intake gaskets. I was told by a local auto repair guy (after he ran a scan with his scanner) that he was getting the code also for the O2 sensor indicating the sysen was lean. He didn't say anything about getting the code for the MAF voltage when he ran the test.. but he suggested that maybe I left a vaccuum line off or loose when I put my intake manifold. That's possible, but I'm almost positive I got everything put back together correctly. But the guy said that code means that there is a vaccuum leak somewhere on the intake manifold and also told me that it could be the head gaskets need replacing. Now I believe the part about a vaccuum leak.... but the head gaskets?????????? Is that a possibility that my head gaskets are leaking air into the engine somehow and bringing this code up (and my engine STILL running with a leak like such)???

I was getting code 157 before I took off the intake manifold and did the work, and now I'm still getting code 157 along with 176. So I also know that the MAF works in conjuction with the O2 sensors so I ordered a brand new Pro-M 80mm MAF earlier this week hoping that fixes at least the code 157. It's also be great if my current MAF is causing the code 176 to come up also and me replacing the MAF also fixes that problem. What does it sound like to you guys? Could a bad MAF trigger code 176? And should the new MAF cure at least my code 157 problem? The last thing I want to do is change the head gaskets on that car. I think I'd honestly find a nice 3.2 and swap it with my 3.0 if it came down to that. But I have 129k on this motor now and it runs so nicely!! I've put all kinds of additives in the fuel and oil since I've owned it and that really brought the motor back to life. I'd hate to have to get rid of the whole motor simply because I don't want to change out the head gaskets. But then again, I also wouldn't mind the 3.2 because it has more potential. Well let me know what you guys think if you have a few minutes to spare. Thanks!!

-Andrew Grayson

 

[AutoSHO]

Are you running a K&N?

 

[92ShoOff]

Hmm... come to think of it I forgot I do have a K&N air filter I just put in about 500-1,000 miles prior to getting the light. But it's the K&N panel filter that goes in the factory air box... it's not a conical filter or anything. Might this K&N panel filter be the problem?

 

[AutoSHO]

Yeah, the K&N coats the MAF filaments with oil and causes the sensor to read a lower airflow than is actually entering the engine. This causes the car to run lean. Clean the MAF with some electrical contact cleaner, and you'll probably find that it takes care of the CEL.

K&N's are not good for these cars... The MAFs are very sensitive.

 

[92ShoOff]

Okay thanks for the info on that Chris. Yeah I didn't know any better about those K&N's... so my bad on that one. Now the conical filters that come with the 80mm Pro-M MAF... do those filters have oil on them like the K&N's do? Because mine is supposed to be in next week so i can install it... and I definitely don't need another filter that utilizes oil. I just hope this new MAF and filter combo doesn't give me any problems... because regardless whether cleaning my MAF solves the problem or not I want to put that 80mm MAF on there. Hahaha. Thanks again Chris!

-Andrew

 

[AutoSHO]

The 80mm MAF may use an oiled filter, but I am not sure. I would assume (hope) that Pro-Flow would put on a filter that doesnt make their product junk after a few thousand miles. I've never heard of any trouble with it.

The 80mm may still throw a code on long highway deceleration for 157 - MAF Voltage too low - It can be ignored. You shouldn't still get a lean code, however, unless either your fuel pressure is low, you have a clogged injector, or the oxygen sensor is bad.

 

[MichaelH]

I run K&N on both my SHOs and have no problems. I love 'em. The ATX has the drop-in, while the MTX has the cold air snorkel with separate filter. I believe the problem arises when you over-oil the filters and some oil gets through.

I have some questions. When you get the 176, is the car up to operating temperature? The O2 sensor must be arount 600 degrees before it operates correctly, so if the engine's cold you could get a faulty reading.

Next, are you getting only 176? If so, maybe it is the sensor. Remember, you have two, a front and rear. This is for the front. Maybe the only thing you really need is a front O2 sensor.

 

[92ShoOff]

Well see, my filter came pre-oiled so I didn't oil it myself before installing it. And it wasn't over-oiled from the factory when I got it, so I dunno what the problem good be. I put the Fram back in today and cleaned out the MAF sensor so I'll see if I get the CE light tomorrow.

But yeah the CE light is intermediate. It doesn't come on and stay... only stays on for a few seconds at a time. From what I notice it only comes on while I'm driving... never while I'm sitting still I don't think. But the engine is always at operating temperature when the light comes on, and I have only scanned the codes after bringing it back for a drive and getting the light. So yeah the engine has always been at operating temperature when I check it.

I'm not only getting code 176, no. I'm getting code 176 and code 157 (MAF circuit below minimum voltage). I'll have to see if at least the code 157 goes away tomorrow. Hopefully both of them go away though since the O2 sensors work with the MAF. But I had the O2 sensors check just yesterday and they work fine. They were installed like only 12,000 miles ago so they're definitely not already bad. Well let me know what you think.

Thanks!,
Andrew

 

[MichaelH]

Hmm. Well, I had an intermittent CE on my '93 and it turned out to be the O2 sensor and again on my '95 ATX. That's because when they're failing they work intermittently.

Anyway, something to think about, as the O2 sensor can become damaged under certain circumstances. What makes the sensor even more suspect is that you aren't getting a 172, which is the rear O2 sensor, only the 176 for the front.

 

[wood_e]

You shouldn't still get a lean code, however, unless either your fuel pressure is low, you have a clogged injector, or the oxygen sensor is bad.

Or a vacuum leak...

 

[Zap]

FWIW, If the O2 sensors are new, you could be experiencing problems related to a dirty connector. My '95 MTX had an intermittant O2 lean condition, just on one bank. It was very sporadic, and so when I was under the car, I went ahead and cleaned the contacts on the in-line connectors. I had new O2 sensors at the time, but I decided that I would save them for another time if it just cleared up, and it did! I have not seen the light again in quite some time, and since these sensors work on a relatively low voltage, from what I've been told, dirty connectors can cause all sorts of funky problems with them.

 

[Axianator]

Out of curiosity, Andrew, when does your CE light usually illuminate itself - during high-load and/or full-throttle situations, or is it seemingly random? Have you checked your Y-pipe and the area where it joins to the exhaust manifolds for leaks?

 

[92ShoOff]

Hey sorry I haven't been back on here for a few days guys.. I have been having to go work out of the area for the past few days but I'm back in action now. Yeah I will definitely have to check the connections of my O2 sensors. It'd be great to find out that all it was was a dirty contact or something. Not likely though for me I'm sure... nothing has been an easy fix for this car yet.

But no, the CE light doesn't only come on under heavy load or full throttle. Just randomly really. I can be cruising steadily anywhere between 40-70 mph and get the light. I don't think the light has illuminated while I've been at a stop though.. although I did come to a stop at a traffic light while the CE light was on and it stayed on while I was sitting at idle. So I don't know if that makes a difference about it not coming on while sitting still or not.

Well I will be replacing my MAF this weekend and I'll crawl under the car and see if the flex pipe has a leak or anything. The flex pipe was also repaired back when the O2 sensors were replaced... so I'm sure it's also possible that buy now the Y-pipe could be leaking at one of the joints. I wouldn't mind that too much because that would give me an excuse to "have" to get the ShoShop Hi-Flow Y-pipe. I'm just hoping for a simple fix. I just want to hear that the head gaskets wouldn't cause this engine code in any way, shape, or form (as described on my very first post on the top of this page). So can someone shed some light on that for me please?