Help With Engine Codes Car Code 172 HEGO (HO2S) sensor fault/lean

DJiCE

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Apr 2, 2003
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Need Some help to deciper the following codes:

I get the Following Fault Codes For Sensors ( I tested it with getting engine to running Temp so I believe this what causes these codes)

CODES: 116 - Engine coolant temperature higher or lower than expected
636 - Transmission Oil Temperature higher or lower than expected

NOW CODE STORE IN MEMORY

CODE : 172 HEGO (HO2S) sensor fault/lean

What does this mean?

Here are my symptons:

When cold it trembles a bit, idle not smooth
After it warms up ~ 5 to 10 mins engine runs smooth.
Durring the cold start when I accerate egine bogs a bit, like it can't breathe.

Something weird that never happen is I see water exiting my exhaust pipes.
I also notice my high pressure line to fuel rail was comming loose so I re tighten it.

Any Help much appreciated.
 
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HISSIN50

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Check the ECT voltage when the engine is cold and then once at temp.

When at ~50*F, the sensor (KOEO) should show about 3.50V (dont test it below 50* - the results are not accurate).

At 180*F, you should see about .75 V.

For both tests, you dont need to have the car running if you're worried about moving engine parts. Just have the key on.

The ECT code can generate an O2 code, so the ECT is the place to start.
 

DJiCE

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OK, How easy is it to get to the ECT sensor? location on the manual says it's at lower intake. Included Pic. Laso found instructions on testing it at:

TESTING ECT SENSOR



Since it was nice out today I cleaned the maf sensor and re oiled the K&n Filter.
Still drying the filter so couldn't test if that helped.

tomorrow hopefully I will test the ect sensor
 

HISSIN50

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My testing method incorporates part of your vehicle's wiring, which the resistance testing does not. You can do the resistance test but the ECT circuit can still be bad. If testing it plugged in, you atleast can see that the thermistor carries a load and unless the wiring from the ECT to the EEC is bad, it should be copacetic.

The chart in your link shows more graduations of the voltage values (earlier I only provided the two most useful ones to me).

Good luck.
 

Chythar

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Aug 26, 2004
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If your ECT is bad, the engine will likely run rough - the computer adjusts fuel based on the engine temperature. Hissin's testing technique won't lead you wrong, helped me diagnose a bad ECT sensor. The sensor is screwed into the front of the metal coolant line that leads back to the heater core, pretty easy to get to.

Don't know much about diagnosing the transmission code, has the transmission been shifting different as of late? Is the fluid level low?

Water in the exhaust is relatively normal, it's just water in the air condensing in the hot exhaust pipes. Since you're running lean (code 172), the exhaust will be hotter than normal and you'll get a bit more water. It's normal, nothing to worry about.
 

DJiCE

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Ok I did the Resistance test, but I was not able to get any voltage from the sensor only resistance.

This is how I tested it for Voltage and resistance.. With key on position and disconnected harness I hook up volt meter and was able to get resistance but no values for voltage the 2 pins on the sensor.

Do I get voltage from the sensor pins? how do I test voltage?

here are my results:

cold got 58.1 Kohms 0 volts
then a bit warmer 24.3 0 Volts
warmer 7.9 Kohms 0 Volts
Near "N" Normal 3.3 Kohms 0 volts

Trans runs great, level is fine and very clean.. That error code may be because I ran the code scanner at cold did not warm up car?
 

99FiveOh

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May 20, 2006
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Ok, you're not going to get ANY voltage from the sensor if your car isn't giving it any, meaning, you need to plug the sensor back up and probe the wires.
 

DJiCE

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UPDATE: 2-9-09 Ran code reader this time at normal operating temps:

Now I Get NO SENSOR ERROR CODES:
CODES 116 - Engine coolant temperature higher or lower than expected - GONE
636 - Transmission Oil Temperature higher or lower than expected = GONE

BUT NOW HAVE THE FOLLOWING CODES STORE IN MEMORY:

CODE : 172 HEGO (HO2S) sensor fault/lean
CODE : 332 Insufficient EGR flow detected - NEW CODE

Should I replace the EGR VALVE?
 

99FiveOh

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May 20, 2006
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Take the EGR off and check the rubber diaphram, they crack alot of times then won't work period! I'm glad I live in a state that doesn't check for them.. mine will be coming off as soon as I score a fox TB and cable!
 

HISSIN50

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Also make sure you didnt remove or break the vac line to the EGR, and that the position sensor is plugged in. When a code comes out of nowhere after not having been there, a lot of the time it's something that was disco'd or broken during other work.

For a quick EGR valve test, you can simply let the car idle and disconnect the vac line to the EGR. Put a spare vac line on the EGR vacuum nipple and apply about 6" of vacuum to the line (I just use my mouth, but a Miti Vac works. Guys, insert your jokes here. Ha ha, I said insert too). You can see the diaphram move and the engine will start to stall. Be careful while working around a running engine and all that.
 

DJiCE

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I finish testing the ect sensor,
here are the results (Voltage):

Disconnected connector and test for voltage got 3.5V
With connector plugged in I got 1.61V (Engine cold)
"" "" (Engine Mid Warm) .78V
"" "" (Engine at normal temp) .12V

So far I cleaned MAF, used Chevron Fuel Injector Cleaner it's running a bit better but not perfect.

I also cleared the codes and will see if they pop up again so far no check engine light.

Next on my list is replace spark plugs and check for vacuum leaks.
 

HISSIN50

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I finish testing the ect sensor,
here are the results (Voltage):

Disconnected connector and test for voltage got 3.5V
With connector plugged in I got 1.61V (Engine cold)
"" "" (Engine Mid Warm) .78V
"" "" (Engine at normal temp) .12V

So far I cleaned MAF, used Chevron Fuel Injector Cleaner it's running a bit better but not perfect.

I also cleared the codes and will see if they pop up again so far no check engine light.

Next on my list is replace spark plugs and check for vacuum leaks.
How did you do voltage testing with the ECT disconnected? Was this the 5 volt feed into the sensor's pigtail? If so, you have an issue.

You can see that all of your readings are phase shifted high. Figure out why your VREF is only 3.5 volts instead of 5.
 

DJiCE

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Bloomfield, NJ
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Yes I got the 3.5V with the pigtail disconnected and probed the socket connector with key on position.
Rest where with the sensor and pigtail connected and back probe the connector for voltage

Will have to re-test and make sure, thanks once again.
 

Chern_889

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Oct 22, 2006
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I had the same lean code on both the left and right banks when i first bought my car, finally narrowed it down to an extremly dirty maf, cleaned it and codes went away, with it also came about a 100HP increase on the seat-of-the-pants dyno
 

DJiCE

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Bloomfield, NJ
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here's an update after re-testing ECT and Codes:

1st after clearing codes, they cam back two days latter:

SENSOR TEST OK ;>
Code Store in memory: 172 HEGO (HO2S) sensor fault/lean

Now for ECT TEST:

Disconnected connector and test for voltage got 4.57V
With connector plugged in I got 3.71V / 17.1K Ohms (Engine cold)

2.05V / 7.09K Ohms
1.15V / 4.8K Ohms
.77V / 2.9K Ohms (Very Close to Normal Temp)

Now I believe ECT is OK, So can I say problem most Likely Oxygen Sensor?
 

HISSIN50

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here's an update after re-testing ECT and Codes:

1st after clearing codes, they cam back two days latter:

SENSOR TEST OK ;>
Code Store in memory: 172 HEGO (HO2S) sensor fault/lean

Now for ECT TEST:

Disconnected connector and test for voltage got 4.57V
With connector plugged in I got 3.71V / 17.1K Ohms (Engine cold)

2.05V / 7.09K Ohms
1.15V / 4.8K Ohms
.77V / 2.9K Ohms (Very Close to Normal Temp)

Now I believe ECT is OK, So can I say problem most Likely Oxygen Sensor?

Your warm-voltage reading looks ok. You cannot take resistance readings with the sensor plugged in.

Run over the rest of the items on your car that can cause a systemic lean issue (vac leaks, dirty MAF, low fuel pressure under demand, etc etc).
 
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