98 Rodeo - CEL P0171

[Rutty]

Have a '98 Rodeo, 127K miles. CEL light came on and off for awihle, and eventually just stayed on. Ended up as P0401 (Decreased EGR Flow). Cleaned the EGR ports and all is well.

A few weeks later CEL light again... intermittent at first, now stays on. Finally had it red at AutoZone. P0171 - Fuel Trim System Lean Bank 1. Idles a little rough, but runs smooth when accelerated. Every now and then it feels like it wants to stall (when idling) but it has never stalled.

Most of the posts I have seen here (and in 4x4Wires's forums) for P0171 code are usually associated with 1 or more other codes (P0172, P0174, P0175). I don't have any other codes, just this one.

AutoZone guy and friends think its dirty injectors. Tried running with Techron and RXP Gas Kicker. Neither did the trick.

Other sites seem to suggest O2 sensor and/or intake manifold gasket (IMG). But usually they are associated with other codes also.

Thoughts? Try getting an fuel injector service done (dealer said $140 - good price?) Try to do the O2 sensor (is that hard to replace)?

CELs are an automatic fail on state inspection (which is due this month), so any help would be greatly appreciated!

[Rutty]

Forgot to mention, its a 3.2L, v6.

[international bus]

NotesDTC P0171 -Fuel Trim System Lean Bank 1



Circuit Description
To provide the best possible combination of driveability, fuel economy, and emission control, a "closed loop" air/fuel metering system is used. While in "closed loop," the powertrain control module (PCM) monitors the Bank 1 HO2S 1 and Bank 2 HO2S 1 signals and adjusts fuel delivery based upon the HO2S signal voltages. A change made to fuel delivery will be indicated by the long and short term fuel trim values which can be monitored with a scan tool. Ideal fuel trim values are around 0%; if the HO2S signals are indicating a lean condition the PCM will add fuel, resulting in fuel trim values above 0%. If a rich condition is detected, the fuel trim values will be below 0%, indicating that the PCM is reducing the amount of fuel delivered. If an excessively lean condition is detected on Bank 1, the PCM will set DTC P0171.

The PCM's maximum authority to control long term fuel trim allows a range between -15% (automatic transmission) or -12% (manual transmission) and +20%. The PCM monitors fuel trim under various engine speed/load fuel trim cells before determining the status the fuel trim diagnostic.

Conditions for Setting the DTC

• No scan tool test is being run.
• None of the following: EGR DTCs, HO2S DTCs, (response, transition, open, low volts, no activity), MAF DTCs, TP sensor DTCs, Map DTCs, IAT DTC8, canister purge DTCs, EVAP DTCs, injector circuit DTCs, or misfire DTCs.
• Engine coolant temperature is between 25°C and 100°C (212°F).
• Intake air temperature is between -0°C (-0°F) and 120°C (248°F).
• Manifold absolute pressure is between 24 kPa and 99 kPa.
• Throttle angle is steady below 95%.
• Vehicle speed is below 136 km/h (85 mph).
• Engine speed is between 400 and 6000 RPM.
• Barometric pressure is greater than 72.5 kPa.
• Mass air flow (MAF) is between 2 g/second and 200 g/second.
• Ignition voltage is above 9.5 volts.
• Fuel system is in "closed loop."
• Canister purge duty cycle is greater than 0% if on.

Action Taken When the DTC Sets

• The PCM will illuminate the malfunction indicator lamp (MIL) after the second consecutive trip in which the fault is detected.
• The PCM will store conditions which were present when the DTC was set as Freeze Frame and in the Failure Records data.

Conditions for Clearing the MIL/DTC

• The PCM will turn the MIL "OFF" on the third consecutive trip cycle during which the diagnostic has been run and the fault condition 8 no longer preeent.
• A history DTC P0171 will clear after 40 consecutive warm-up cycles have occurred without a fault.
• DTC P0171 can be cleared by using the scan tool "Clear Info" function or by disconnecting the PCM battery feed.

Diagnostic Aids
Check for the following conditions:

• Poor connection at PCM - Inspect harness connectors for backed-out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal-to-wire connection.
• Damaged harness - Inspect the wiring harness for damage. If the harness appears to be OK, observe the Bank 1 HO2S 1 display on the scan tool while moving connectors and wiring harnesses related to the engine harness. A change in the display will indicate the location of the fault. Reviewing the Failure Records vehicle mileage since the diagnostic test last failed may help determine how often the condition that caused the DTC to be set occurs. This may assist in diagnosing the condition.

Test Description




Number(s) below refer to the step number(s) on the Diagnostic Chart.

1. DTCs other than P0171 and P0174 may indicate a condition present which may cause a lean condition. If this is the case, repairing the condition which caused the other DTC will most likely correct the DTC P0171/P0174.

1. If the DTC P0171 test passes while the Failure Records conditions are being duplicated, the lean condition is intermittent. Refer to Diagnostic Aids or Symptoms for additional information on diagnosing intermittent problems.

[2000izusu]

classic for my 2000 with the 3.2 to throw a po 171 when the i.m.g. is going south. has thrown that code all three times my i.m.g. has failed.

[Rutty]

Thanks 2000isuzu... Is it best to replace the upper and lower IMG or is it often one or the other? I'm a complete novice - is this something I can do myself, or best to let someone trained handle it?

[2000izusu]

it is the lowers that are in question. very common occurrence on 98 + 3.2L.
read up in the F.a.Q section at the top of the forum. procedure is listed and common codes associated with it also are up there. i did not do mine myself. but it looks a little beyond a diy'er. you have to have specific torque on the new gasket as well as take the egr apart which requires a homemade shortened wrench. it is all in the F.A.Q. good luck! mike

p.s. while you got the intake out. you will want to replace the thermostat. it is buried under the plenum on 98+ models. also check the tubes under the intake for coolant leakage. just prevenative.

[Rutty]

Thanks again for the help... One last question. What would you think is a "fair price" (parts/labor) for this work (IMG, O2, and thermostat) at a non-dealer? Called local Isuzu dealer (Dallas suburb) and he said ~$400 just for IMG. Seems kind of steep!!