1999 Honda Civic ECU 0172 and mileage

MAYNARDSCT

MEMBER
1999 HONDA CIVIC
4 CYL
FWD
AUTOMATIC
150,000 MILES

Trying to diagnose my sons "toy". Trouble code is 172, system running rich trouble code and his mileage sucks. He took it to a shop and they found a vaccum leak and repaired that and cancelled code. It came right back. They said his injectors may need cleaned. The car lags bad on acceleration and gets bad mileage. A cold air intake was installed on this and I am wondering if the Mass airflow has been removed and may be causing it? There is a small probe / sensor that is stuck in the rubber coupler between the intake pipe and throttle body through a small slit in the rubber coupler and it is a 2 wire probe. Car runs smooth but is defintely has no power and is running way too rich. Any suggestions?

5 Replies

KHLOW2008

MECHANIC
41,814 POSTS

Hi maynardsct,

Thank you for the donation.

Go through the following and see if you need help on any of the procedures.

If DTC P0172 (system too rich) is set, check for:

Fuel pressure regulator clogged or stuck closed.
Clogged fuel return line.
A leaking fuel injector.
Fuel octane level less than specification.
A deteriorated primary HO2S-1.
Insufficient EGR system flow (D16Y5 engine).
A leaking or stuck open EVAP purge control solenoid valve.
Valves incorrectly adjusted.

Honda does not use MAF. A MAP sensor is used and is attached to the top of the throttle body. The item plugged into the air intake hose is the Intake Air Temperature sensor.

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Wednesday, June 3rd, 2009 AT 2:14 PM

MAYNARDSCT

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3 POSTS

Looks like we should get the fuel system gone through first. Probably the most likely culprit. How would I go about checking the HO2S sensor, any readings or electrical tests I could do and is that the one attached at the manifold? Have to see if I can locate a book for this car.

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Wednesday, June 3rd, 2009 AT 3:41 PM

KHLOW2008

MECHANIC
41,814 POSTS

A scanner would be required to test the HO2S as it has not completely failed which would trigger a code. Possibility is it has deteriorated.

Here are the test procedures.

Start engine and run at 3000 RPM with no loads and transmission in Park or Neutral until radiator fan comes on. Using scan tool, check primary HO2S-1 output voltage. If voltage stays at less than 0.3 volt or more than 0.6 volt, replace HO2S- 1.

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Thursday, June 4th, 2009 AT 9:23 AM

MAYNARDSCT

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3 POSTS

Thanks again. One more question today. Could you give me the valve clearances? I am going to install a new timing belt tomorrow and that would be a perfect time to check that while we have it in the shop. Thanks again.

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Thursday, June 4th, 2009 AT 9:41 AM

KHLOW2008