P0171 to p0172 2003 trailblazer 4x4 6 cyl

I think u should have the engine checked for avaccum leak or a sticking fuel pressure regulator!

I am asking my associates fro ideas BUT nothing but questions... seams to be a rehash of what I asked already.. One question that was asked several times was - what is ECT looking like?

The ECT (engine coolant temp ?) is running 195 -200 matches the gauge in the dash . I checked for vacuum leaks with the Carb cleaner while it was running -nothing . Discover more Fuel tank fuel tank Forum The fuel pressure checked fine and did not leak down way back inthe beginning . if it was sticking would it make the LT specs higher ?? And how would I check it for sticking ?? One thing I noticed the other day when I turn the engine off and key back on the LT fuel trim reads 7.0 not running . Wonder if this points to anything ??

Can you read my last post ? Also is there any chance one of the O2 sensors are causing this . Now the p172 codes come right back on after a few miles of driving if I clear it .

Sent two previous posts . Guess there is no other ideas ? I checked and answered your questions you had . Thanks for your help .

Hello ? How you all doing . Never did figure this out why the rich code stayed on ? Now that the weather cooled off ? The code went out about a month ago about when the weather cooled down . It went out one day right after we hit a bad bump in the road ,but it was also very cold outside for the 2nd day . It came back on one more time when a day got up into the 80's . I cleared the code two days later when it cooled off again and been driving it for two full weeks and no codes . The weather has stayed cool around 60's . This code would never stay off during the hot weather .it would come on within 20 miles after it was cleared all summer . Anybody have any ideas ??? I am thinking it is one of the 02 sensors ,but which one ? Thank you .

repeat #PIP3561 Subject: SES Light Due to DTCs P0171 and P0172 - Monitor Fuel Pressure - keywords 4.2 4.2L CEL controls engine LL8 MIL repeat #PIP3561 - (10/06/2005) Models: 2004-2005 Buick Rainier 2002-2005 Chevrolet TrailBlazer 2002-2005 GMC Envoy 2002-2004 Oldsmobile Bravada 2005 Saab 9-7x with 4.2L Engine (VIN S - RPO LL8) -------------------------------------------------------------------------------- The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI. Condition/Concern: On rare occasions, a SES light may be experienced due to DTCs P0171 and P0172. Typically, there will not be any performance concerns reported and the DTCs will not set at the same time but upon inspection, both DTCs will be stored in history together. Recommendation/Instructions: If the SI diagnostics do not isolate a cause for the above concern, perform the following suggestions as necessary: •Ensure that the latest PCM calibrations are present. Some models have calibrations available to address certain P0171 and/or P0172 DTCs. •Inspect the oxygen sensors for proper operation and possible sensor contamination. If incorrect oxygen sensor operation is noted, replace the oxygen sensors as necessary. If the sensors are contaminated, inspect for contaminated gasoline, coolant consumption, or previous repairs where silicone sealant may have been used. Repair the cause of sensor contamination and replace the oxygen sensors as necessary. Replacement oxygen sensors contain product improvements. •Check for a skewed MAP sensor at idle and KOEO. The PCM uses the MAP sensor as a fuel control input since this engine does not have a MAF sensor. If the MAP sensor is skewed, the PCM may mis-fuel the engine. If necessary, compare the MAP sensor value to a known good vehicle to confirm sensor accuracy. If a skewed MAP sensor is found, replace it. •Inspect for obvious vacuum leaks at the throttle body, intake and PCV hose between the #3 and #4 intake runners. If there are no vacuum leaks found, remove the throttle body and inspect the throttle body gasket to make sure that it is not rolled. A rolled seal could cause an intermittent or hard to find vacuum leak. If the throttle body gasket is rolled, replace it. •Clean the fuel injectors using the procedure found in bulletin 03-06-04-030. If cleaning the fuel injectors corrects the concern, refer to 04-06-04-051A, which relates to maintenance cleaning of the fuel injectors to prevent a reoccurrence. •Check for a skewed ECT or IAT sensor by making sure that they are within a few degrees of each other prior to a cold. If one of the sensors is skewed, replace it. •Clean the throttle body bore and the throttle valve plate using a clean shop towel with GM top engine cleaner or an equivalent product. •If there is no problem found, this may be due to the fuel pressure intermittently decreasing below specification. If fuel pressure decreases, the PCM will increase the injector pulse width to compensate for the lean concern, which may eventually set a P0171 (lean) DTC. If the fuel pressure increases again so it is in specification, a false P0172 (rich) DTC may eventually set because the PCM is only allowed to decrease learned fuel control values in small increments each engine run cycle. Check fuel pressure by following the SI procedure. If a momentary drop in fuel pressure is noted or suspected, inspect the fuel pump circuits for poor connections, terminal tensions, poor ground, etc... If there is no problem found, replace the fuel pump module. Note: Disconnect the battery for several minutes after any of the above repairs are performed. This will reset the volatile and non-volatile fuel control values that may have been learned by the PCM. Road test to verify repairs. Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information. WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION © Copyright General Motors Corporation. All Rights Reserved.

Subject: Service Engine Soon Light On, P0133, P0172 (Reprogram PCM) #04-06-04-053 - (07/20/2004) Models: 2004 Buick Rainier 2003-2004 Chevrolet Trailblazer 2003-2004 GMC Envoy 2003-2004 Oldsmobile Bravada with 4.2L Engine (VIN S - RPO LL8) -------------------------------------------------------------------------------- Condition Some customers may comment on the Service Engine Soon light coming on and no apparent vehicle driveability condition.. Upon investigation, the technician will find diagnostic trouble codes P0133 or P0172. Correction Reprogram the PCM with the latest calibration available. The new calibration will be released beginning with TIS satellite data update version 2.5 for 2004 available February 2004. As always, make sure your TECH2® is updated with the latest software version. Warranty Information For vehicles repaired under the applicable 8 year or 80,000 mile (130,000 kilometers) emission controller warranty, use: Labor Operation Description Labor Time J6353 Module, Engine Control - Reprogram 0.4 hr GM bulletins are intended for use by professional technicians, NOT a "do-it-yourselfer". They are written to inform these technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions, and know-how to do a job properly and safely. If a condition is described, DO NOT assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See your GM dealer for information on whether your vehicle may benefit from the information. WE SUPPORT VOLUNTARY TECHNICIAN CERTIFICATION © Copyright General Motors Corporation. All Rights Reserved.

PI072 rich fuel code This code only hits when ambient temps get into the 80's or higher . I have checked everything I can possibly think of with a gm techs advice . Fuel Psi is good , no vacuum leaks , tried new map sensor . This truck does NOT have a MAF sensor . During the winter months the code gos away and only came on 1 time in December when temps outside got to 80's , then went out when it got cooler until last week . This has happened for 2 winters now and this is 2nd summer since we bought it . The fuel software was updated also at dealer . It only codes when it gets hot ambient temps -no lie . It's crazy . The gm tech looked at the short term and long term fuel readings and were ok too . Does anybody have any idea ??? Thank you for any help .

I think you have a vacuum leak somewhere. It would also explain why your door mode actuator is not working and is defaulted to defrost. It is also possible that your intake manifold is leaking somewhere. Check for vacuum leaks, keep it simple, get down to fundamentals. kev2 is getting way too in depth for a DIYer. If you cant find it on the basics take it to a shop. Check Vacuum Lines for Leaks!

I have checked for vacuum leaks many times and with ether and carb cleaner . The mode actuators are electric . Don't think there are any vacuum lines going to dash .

In the past I have seen plastic intake runners crack or the gasket fail. If this happens on a single intake runner it can cause a p0171 lean code. The ECU correction for this can then cause a p0172 system rich code. Small cracks in an intake runner of single intake runner gasket can be very hard to find. Fuel trims are high because the ECU is trying to correct for an initial rich condition. If one cylinder is receiving unmeasured air then fuel injection pulse width (quantity) will increase to all cylinders to correct for the condition. This can cause a p0172 rich condition if it can not be corrected within the limits of the fueling table. That' I've got for you. Double check the intake for manifold and plenum for leaks.

Ok thank you so much . Couple questions : How would I double check this ? And not sure what am intake runner is ? This engine is all new to me . I am a heavy diesel truck mechanic . Appreciate all your Info . Is there a "you tube" on this Intake and plenum leak checks ?

A failled 02 is a possible yes but it's not common for them when they fail to generate a rich code and then a lean code! they tend to get stuck on one bias or the other but it is possible!

I would suggest getting a professional diagnosis at this point. Intake manifold leaks can be tricky to find without the proper know how. There could also be an issue with the air pump valve if your vehicle is equipped with one. This problem is definitely killing your fuel economy. If you get a professional diagnosis and repair estimate I can ensure that you are getting a fair price on parts and labor.

Its been at a dealer 3 times . Only thing they keep telling me is that my only option is to wait for a data recorder to have in the vehicle while driving until it codes . Then maybe they can see why ? Ha ! I have been waiting for a year now for it to come available . They said one time it broke and had to be sent out to be fixed . Also just for the record the weather has been rainy and cooler for the last few weeks 60's to 70's outside temps and it has NOT coded at all . But sure thing when it gets into the 80's or higher it will code instantly the PI072 rich code . This don't make sense ! If it was a vacuum leak it would code all the time , but it only codes when temps go up higher outside . It stays off in all the colder months and comes on only in hotter summer months . Some thing is definitely 100% related to the ambient temps . Its hard to believe this issue has never happened to anyone else with this type of engine ?? I do have a friend who is ready to hook up to it with a very good tool and can perform real time stats . Now we are just waiting for hot weather here in NC , because now it's still off . If you really think a vacuum leak could make it act up in hotter weather , then I will spend the money on diagnostics again , but I don't have much confidence in the Dealer .

In my opinion and experience a lean condition like a vaccum leak doesn't generate a rich dtc! it's just the opposite in fact! Because of the increased positive fuel trim to bring the mixture back closer to stoich when it has a vaccum leak or low fuel pressure it should max out the corrective factor and code for lean! It seems weird that at one point your long term fuel trims were like positive 17 yet it didn't generate a lean dtc po171 but a rich po172? To flip flop like that in my opinion has to be an issue with fuel delivery! A bad fuel pump can under deliver fuel volume which makes the truck lean and conversly if the presure regulator was bleeding pressure off under load or sometimes sticking and spiking the fuel pressure the same way a restricted return line does then that could explain the rich code but your fuel trims then should be going negative in an attempt to remove fuel not still show positive! Firstly I know you've said they've recalibrated the pcm but are you sure the pcm is updated as per the tsb? If it has been then I'd suggest everyone that's working on this truck forget about the code for a sec and use the fuel trim patterns and what they're doing at the time to point to the issue! High positives not enough fuel, high negatives, too much fuel! It's really not all that complex and fuel pressure and flow need to be checked both static and under load on a roadtest! Under WOT if the upstream 02 sensor won't hit .9 volts then it's lacking fuel, if it will hit .9 then i wouldn't expect it to code for a lean dtc! Almost all cars stil go into open loop status at WOT which means they ignore the 02 correction factor so if it'll hit .9 volts then I wouldn't even suspect the 02 as being a potential cause! Like I said 02's can fail and stick to a bias but for them to intermittentl stick to one and then the other is super rare! I've never seen one do it! To be that lazy I'd think it'd be glaring obvious on the scanner! A good tech that can graph them can tell in two minutes if the 02's are bad or not!