I own a 2004 Blazer with 36,700 miles on it. It runs very well. Recently, the service engine soon light has been coming on and off intermittently.
I changed my fuel cap several times and the light would go off and then come back on a few days later, then off again. I brought it in to get inspected and it failed
with codes P0171 and P0174. System too lean Bank 1 and Bank 2. The fuel filter was replaced and the light came back on and then went off and now its on again.
I am bringing it to the dealer this week. Any ideas what I am looking at? The repair shop I brought it to did a diagnose test and there was nothing wrong with the sensors but it showed a problem with the fuel system.

 

clean the MAF sensor, check for vacuum leaks. if that doesn't fix it, have the fuel pressure tested (including a leakdown test).

http://www.obd-codes.com/trouble_cod...gen-sensor.php
http://www.obd-codes.com/trouble_cod...gen-sensor.php

 

Is this expensive and time consuming? Would it be covered under the warranty?

 

you could probably do it yourself fairly easily. i've never done it, maybe someone else can post instructions.

 

If the car is under warrenty, it would be silly to take chances and work on something you may not be familiar with. Learn from what is done when you bring it in. It will still be YOUR decision as to wether they actually do the work or not. If something major is wrong however, you do not want to be the one responsible for introducing parts to an automobile that may void this warranty.

The true main experience of having a warranty is to let the dealer handle just about everything while it is coverred. The problem with not letting them handle service is that they know and can tell when parts are used that are non standard or not used by dealerships.

The fun part happens when something major is wrong. If you have somehow given the dealer a way OUT of his responsibility, by perhaps giving them the opportunity to void it.... lets put it this way, you may save 50 or 75 bucks if its a simple problem, by doing it yourself. But if its not something you can fix, you may have a bigger bill by using what they might consider an inferior part.

A normal relationship with your dealer should not lead to them voiding a waranty just because you do some simple maintanance, like oil changes or filter changes. But you indicate not knowing what the trouble is. Normally a qualified chevy dealer can give you a good and accurate reason and an estimate. They will also let you know how much is coverred or not coverred by the waranty. Again, then the decision is still yours.


In other words, if i had a waranty, I'd visit the dealer first. If nothing else, all their work becomes part of the vehicle history should further problems arise after they work on it.

 

Remove the O2 sensors and clean them w/ electrical parts cleaner. I did that when mine threw a lean bank 1 code. No problems since. Good luck.

 

Check these out and see what ya get. there are a few links in these that I didnt go to and copy/paste for obvious space constriction issues. At end first "Go to" is if "yes" second is if "no". The P0174 seems to be a FORD code



DTC P0171 Fuel Trim System Lean
Circuit Description
In order to provide the best possible combination of driveability, fuel economy, and emission control, the vehicle uses a Closed Loop air and fuel metering system. While in a Closed Loop, the VCM monitors the oxygen sensor signal voltage. The VCM adjusts the fuel delivery based on a signal voltage. The long and short term fuel values, which a scan tool can monitor, indicates a change made to the fuel delivery. Ideal fuel trim values are around 128; if the oxygen sensor signal indicates a lean condition, the VCM adds fuel. This results in fuel trim values above 128. If the oxygen sensor detects a rich condition, the fuel trim values will read below 128. This indicates that the VCM is reducing the amount of fuel delivered. If an excessively lean condition is detected, the VCM sets this DTC which is a type B DTC.

Conditions for Setting the DTC
No IAC or idle DTCs
No HO2S sensor DTCs
No TP sensor DTCs
No MAP sensor DTCs
No EGR sensor DTCs
No EVAP sensor DTCs
No ECT sensor DTCs
No MAF sensor DTCs
No IAT sensor DTCs
No VS sensor DTCs
No system voltage DTCs
No Misfire DTCs
Throttle position less than 95%
Engine speed greater than 575 RPM but less than 4500 RPM
The BARO greater than 70 kPa
The ECT greater than 0°C but less than 99.7°C
The MAP is greater than 20 kPa but less than 98.9 kPa.
The IAT greater than -20° C but less than 69.7° C
The air flow greater than 3 grams per second but less than 100 grams per second
The vehicle speed less than 85 mph
The average of short term fuel trim is no more than 115.
Action Taken When the DTC Sets

Important
To complete a trip cycle for the fuel trim diagnostic, the fuel trim diagnostic test must enable and run according to the current DTC Will Set When criteria above. A trip is not considered complete until the fuel trim diagnostic has run by the VCM.


When the current DTC initially sets, a software flag indicating an emissions related fault sets for 3 trips. The flag will clear provided the lean condition is no longer present. However, if the VCM detects the conditions for setting the current DTC during a trip while the flag is still set, the VCM turns on the MIL (Malfunction Indicator Lamp). The MIL remains on during all of the subsequent trips until the DTC has been cleared by service or the lean condition has not been detected and the conditions for checking the fuel trim have been met for 3 consecutive trips.

Conditions for Clearing the MIL/DTC
The VCM turns OFF the MIL after 3 consecutive driving trips without a fault condition present. A history DTC will clear if no fault conditions have been detected for 40 warm-up cycles (the coolant temperature has risen 22°C (40°F) from the start-up coolant temperature and the engine coolant temperature exceeds 71°C (160°F) during that same ignition cycle) or the scan tool clearing feature has been used.

Diagnostic Aids
If using the diagnostic tables does not isolate the problem, try monitoring the L. T. fuel trim and fuel trim cell while operating the vehicle under various loads. This may isolate the condition which caused the setting of this DTC.

A condition that causes the DTC P0300 Engine Misfire Detected may also set this DTC; conversely an extremely lean condition which sets the current DTC can cause a misfire at idle and the DTC P0300 to set. If the cause of this DTC cannot be determined and the DTC P0300 is also set, refer to DTC P0300 Engine Misfire Detected .

Test Description
The number below refers to step number on the diagnostic table.

Visually and physically check the items that can

 

Ever change the air filter?????