Why is my service engiine soon light is on?

Tiny
TGUMBYW
  • 2003 FORD F-150
  • 106,000 MILES

I took it to O'Reilly's and they said something about fuel mixture too rich.

Ford said it was the "heated oxygen sensor". Said they had never had one of these situations before and had to look it up in old books. And said that they would order the sensor at a cost of $269 not including this visit. So probably over $300 most likely. I waited a week with no call from Ford, so I went to NAPA.

NAPA doesn't offer to hook up to your computer.

Next, I went to Auto Zone. They hooked up and said it was the mass airflow sensor at the intake/airfilter. They sold me an $8 can of cleaner specific to the "mass airflow sensor" only. I was told to disconnect my negative battery terminal. I did both terminals and cleaned them. I took the filter out and checked it. It was practically brand new. I located and sprayed the sensor. The sensor didn't have any dirt, grass, or refuse of any kind on it, that I could see. Put it all back together after the spray evaporated.

Cranked the engine and the light was off. It stayed off for a while, then came back on after about 100 miles. I don't drive much since I'm currently unemployed from being laid off.

I bought the truck from an individual who said the light had just come on. I have had it only a couple of months and only drove it to work. No long trips, no dirt roads.

The truck didn't have an owners manual in the glovebox. I called the guy and he said if it had one it would be in the truck.

There is some digital readout display on the ceiling that does not illuminate. The guy I bought it from said it was a compass, I think. Any relationship to the "service engine soon" light?

Any

Thank You

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Saturday, February 11th, 2012 AT 9:03 PM

12 Replies

Tiny
RASMATAZ
  • MEMBER

Have the computer rescanned for code/s and post them if any present-

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Sunday, February 12th, 2012 AT 12:17 AM
Tiny
TGUMBYW
  • MEMBER

This is on a printout from AutoZone:

Troubleshooting PO175

OEM Brand: Domestic

Definition: Fuel trim bank two condition

Explanation:

The ECM has detected a rich or lean Air/Fuel ratio condition on engine bank two.

Probable cause:

1. If bank one and two are set together suspect a fuel pressure condition or MAF snsor fault.

2. Failed HO2S21 ( Heated oxygen sensor - Bank 2 Sensor 1 )

3. Ignition misfire condition

4. Fuel injector problem

5. Engine mechanical condition

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Sunday, February 12th, 2012 AT 10:42 AM
Tiny
WRENCHTECH
  • EXPERT
  • 20,566 POSTS

All this information and still no engine size?

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Sunday, February 12th, 2012 AT 1:33 PM
Tiny
TGUMBYW
  • MEMBER

My truck's engine is the 4.6 litre.

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Monday, February 13th, 2012 AT 7:33 AM
Tiny
TGUMBYW
  • MEMBER

My F-150 has the 4.6 Litre engine.

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Thursday, February 16th, 2012 AT 8:19 PM
Tiny
WRENCHTECH
  • EXPERT
  • 20,566 POSTS

You're reading too rich a mixture on the driver's side only. Now you have to determine why. Could be any number of things and needs to be troubleshooted systematically.

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Thursday, February 16th, 2012 AT 8:28 PM
Tiny
TGUMBYW
  • MEMBER

From AutoZone: The easiest and least expensive fix was to start with the cleaning of the MAS sensor. That wasn't the cure, so to troubleshoot this issue systematically, what are the next steps from here to the end?

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Friday, February 17th, 2012 AT 12:57 AM
Tiny
TGUMBYW
  • MEMBER

2. Failed HO2S21 ( HEATED OXYGEN SENSOR - Bank 2 sensor 1 ) This is from the above message, which came from AutoZone's computer scanner. It doesn't sound good. FAILED, never sounds good. Judging from your experience and knowledge, does this mean that my Heated Oxygen Sensor is at fault?

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Friday, February 17th, 2012 AT 1:09 AM
Tiny
WRENCHTECH
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Yep, that could do it. That sensort does the reporting of rich and lean.

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Friday, February 17th, 2012 AT 1:12 AM
Tiny
RASMATAZ
  • MEMBER

So much of the Snitcher telling lies to the computer that the engine is running lean could also be the coolant temperatue sensor locked-up in open loop mode not switching giving fuel when not needed-

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Friday, February 17th, 2012 AT 1:22 AM

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