Code 176 HEGO Sensor Fault LEAN

[danohagen]

Last February, I started getting a Check Engine Light (CEL) on my 1994 Ford Explorer V-6; so I thought as in the past, it’s probably the Oxygen Sensors being that they haven’t been changed in about 80,000 miles. Changed them (2) out and still get the CEL light . I ran the OBD1 Codes and came up with Code 176HEGO (H20S) Sensor Fault Always LEAN.
The light scenario is daily. It goes on after the engine heats up between 2 to 3 miles of driving. There is no adverse or noticeable problem in the engine performance. In fact, I’m getting pretty good gas milage.
In March, I was getting irritated with the CEL light, so I changed out the 1) EGR DPFE Position Sensor Valve, 2) Vacuum Regulator Solinoid for the EGR Valve, 3) The EGR valve, 4) Fuel Injection Cleaning, 5) PCV Valve, 6) Spark Plugs and Wires
Of course now I’m saying that the Explorer probably needed these parts anyway since I fixed everything but the problem. I still get Code 176HEGO (H20S) Sensor Fault Always LEAN :fire: .

OK, now I’m humbled and appeal to all you Garage Mechanics. What do you think the problem is or what would you try next?
Dan

 

[MrShorty]

Question: Is this a memory code, or have you ran the KOER test and it shows up there as well? If you haven't performed the KOER test, I would run it. It can be easier to diagnose from the KOER test. Can I assume it passes the KOEO test?

Point: 176 refers to the left (driver's side) O2 sensor. The fault appears to be isolated to that side.

There are a lot of possibilities. first thing I would check is the wiring from the offending O2 sensor to the computer. Make sure there are no breaks in the wire and that everything is plugged in tightly.

 

[danohagen]

Thanks, I'll double check the O2 Sensor. The KOEO Code was 176 and the KOER Code came up as 136. Same malfunction for the two codes. I don't know much about the MAF Sensor. Could that sensor function cause a lean code on the one side?

 

[MrShorty]

176 can't be a KOEO code, it has to be a memory code (second set of codes output during the KOEO test). Can't test O2 sensors unless the engine's running.

A false KOER 136 could easily be set if the engine and O2 sensor weren't preheated prior to running the test. Is this a possibility?

Bad MAF data can cause lean codes, though I would expect bad MAF to affect both sides and not just one. But, I wouldn't call it impossible. Do you have a specific reason for suspecting the MAF, or is it just a curiosity question?

In addition to bad wiring, a vacuum leak or an exhaust leak on that side could trigger those codes.

 

[danohagen]

The MAF was just a general question. Disregard. The 176 Code is a memory code. I'll test the KOEOand the KOER after work with a nice hot engine and see what comes up.

 

[danohagen]

This Explorer is my Baby and that CEL light is bugging the Bugeebers out of me. Since there seems to be no affect on the car's performance, that piece of black electrical tape over the CEL light seems to help a great deal.....
Now to reality. - Yesterday, I did a KOEO test and came up with the following codes... 000,111,10,176 Memory and a KOER test of 000,6 cyl, 10, 136.
Today, I bought another O2 sensor and replaced the left (drivers side) sensor. In addition, because I am taking care of some over-due preventative maintenance issues, I also replaced the fuel filter since it's been about 35K miles. After replacing the sensor (2nd one in a month on the left side and have changed out the right side last month; now I have a spare!) and the fuel filter, I sprayed carb cleaner (with the engine running) around the manifold and the vacuum lines. There was no indication of any change in engine performance. Now, I take the Explorer out for a test run and as always, the CEL light comes on again between 1-2 miles.

Shorty!!!! With all the due respect that you deserve, what would you try next?

Note: Don't know if it could be associated with the problem , but that gas level sending unit went out about 5 years ago (80,000 miles). The CEL light only started coming on about a 6 weeks ago.

Dan in Southern California.

 

[MrShorty]

Did you check the wiring between the O2 sensor and the computer?
Any exhaust leaks?
What's the fuel pressure (should effect both sensors, but it's worth checking).
If you backprobe the O2 sensor what does it read?
Can you get a scanner? Your '94 should have the ability to talk to a scanner and allow you to see what the computer sees in real time. Might be worth looking at.

 

[danohagen]

"And the culprit is!!!!"

"And the culprit is!!!!"
Took the car in to a shop to diagnose the problem as I am pretty busy and I'm losing patience with this one. The shop did a smoke pressure check and did not find any vacuum leaks so the technician checked the MAF and wiring from some of the sensors to the PCM (Powertrain/Electronic Computer Module). The technicians conclusion and recommendation was that the PCM was bad and suggested replacement for $180 (refurb. part) + $70 labor. Not wanting to spend any more money than I have to at this point, I said I'd most likely take care of it the following week.
I called a dealer and they wanted $245 (New Part) + $45 labor. Autozone wanted $130 (refurb Cardone part) + $85 for the core exchange. I went on-line to RockAuto who carries Cardone PCM and they had the same part for $85 + $75 for the core exchange.
I ordered from RockAuto and 5 days later it was delivered. Took me 15 minutes to install and FINALLY - NO MORE CHECK ENGINE LIGHT . It has been a full week now and everything works.

 

[MrShorty]

Correct, fuel pressure guage would just screw onto the Schrader valve. If you get a Chilton's (or better) manual, they have a little flow chart for testing fuel pressure with specs and everything.
One thought I had over the weekend: Where you have an O2 sensor code for only one side, what happens if you switch the oxygen sensors? Clear the memory code (pull jumper wire during KOEO/CM code output), then test it to see if the code follows the sensor, or stays on the same side. That would be a quick way to see if the problem is in the sensor or not.

 

[Dragon90815]

Thank you Danohagan for the follow up having the exact same issue