OBD II Trouble Codes 0171 and 0174

[awhtx]

My buddy has a 97 Mazda B4000 pickup and the "Check Engine" light came on. We hooked up a code reader and got 2 codes- 0171 and 0174. The book with the reader says these are "Bank 1- Too Lean" and "Bank 2- Too Lean". Any ideas what's causing this? Could this be clogged injectors, oxygen sensor, mass air flow or what? I don't hear any vacuum leaks and all of the vacuum hoses are connected. All help appreciated.

 

[kps36]

that would be both of your O2 sensors. also, when I did mine, as a precaution, I also replaced the Fuel Pressure Regulator. Maybe ****, but a faulty FPR will send new sensors strait to hell !!

 

[vbtruk]

i got lean mixture cosed on my Explorer both BANK 1 & 2 and it turned out to be a vaccum leak!!! You might need to change the intake manifold gasket's!

 

[phxskier]

Had the same codes with my sons. A friend of mine owns a garage and suggested I check fuel filter as he has seen several Fords with that problem. He also suggested that I disconnect both battery cables and connect them together for 12 hours (or so) because that was a hard code to clear. I found the Fuel filter was severly restricted (actually plugged). However, I ignored his second suggestion because I had never had a problem clearing other codes. Well, the check engine light came back on two days later with the same codes. I took his advice, removed both cables, connected them together and left them overnight. That was two weeks ago and may son tells me the light has never come back on. The fuel filter was a lot cheaper than a requlator or pump. Hopefully that is all that is wrong with yours.

 

[ksandman]

Had same 2 codes a year ago and replacing fuel filter took care of it (along with using code reader to clear codes). Now have same problem again (right before inspection due!) and fuel filter change hasn't worked, nor has fuel injector cleaner, HEET, and Premium gas. Will try cable idea next.

 

[rwenzing]

Vacuum leaks are a common cause of lean codes on BOTH banks like you are seeing here.

As mentioned above, leaky intake gaskets can be the cause. Although it can happen to any engine, it is especially true on the 4.0L.

Another place to look is the PCV system. A very common problem is a rubber elbow that splits and leaks, causing P0171 and P0174.

 

[rwenzing]

He also suggested that I disconnect both battery cables and connect them together for 12 hours (or so) because that was a hard code to clear.

Sorry but the info he gave you is total BS.

All trouble codes are cleared in the same way and that is when the PCM has lost its Keep Alive Memory. This happens in less than a minute if the PCM loses its continuous (always hot) power supply from the battery.

There is no need to disconnect the battery for 12 hours and no need to connect the cables together.

 

[Vinniety]

Sorry but the info he gave you is total BS.

All trouble codes are cleared in the same way and that is when the PCM has lost its Keep Alive Memory. This happens in less than a minute if the PCM loses its continuous (always hot) power supply from the battery.

There is no need to disconnect the battery for 12 hours and no need to connect the cables together.

HAHAH Yes i agree rwenzing,,,,that is BS!!! Thats like saying if your car smokes alot put a bananna in the tail pipe for 12 hours. It wil resolve the smoke issue.
HAHAH Sorry not laughing at you but wow even to think a mechanic would recommend that. If there is no power going through the car trust me that in no way can do anything to resolve any issue.

 

[DB_1]

Another vote for head gasket leaks...had those same codes, turned out it was the head gasket.

 

[Glacier991]

Head gaskets is my vote.

 

[RangerRick]

I'm new here investigating a P0171 code and a TPS voltage to low error.
This is a TSB for the Lean errors:
TSB #16094 -- SOME VEHICLES MAY EXHIBIT FUEL DIAGNOSTIC TROUBLE CODES P0171, P0172, P0174, P0175 OR MASS AIR FLOW DIAGNOSTIC TROUBLE CODES P0102, P0103, P0112, P0113. *TT (NHTSA ID #636110, AUGUST 01 2002)

Anyone know anything about the TPS "Low Voltage" thing?

 

[BrooklynBay]

Welcome to this forum! These codes are generally related to leaking intake gaskets. The fix for this is the 00M12 kit. Check # 51 in my list of useful threads for more information: http://www.explorerforum.com/forums/showthread.php?t=177975

 

[RangerRick]

Thanks BrooklynBay!
Side note, it appears Rick Horwitz is my neighbor. I live in Phoenix AZ

 

[BrooklynBay]

How close do you live to him?

 

[RangerRick]

Maybe 40-60 miles?
Anyhow, the Intake Gaskets are not and were not the problem for me.
I R&R'd the gaskets and the same problem exists, no throttle response other than trying to stall (you can not rev the engine).

I use "Proscan" to read the ECU and only once did I see a code for the TPS, I erased the codes and it did not repeat. The only codes are the "Lean" condition which could be due to either a faulty TPS or MAF but with no readable codes I can't plan a course of action.

Does anyone have the actual TSB I posted? I can not find the white papers to read what the TSB is and the repair/work around.

 

[Redtrac01]

I recently cleared the same codes by cleaning out the PCV line to the intake. There was some crud in it, but the biggest problem was the rubber elbow at the intake. It had a crack in it and a buildup of crusty hard crud partially blocking the passage. Replaced elbow, cleaned tubes, cleared codes and problem went away. Check all of those lines and clean and replace as necessary.

 

[RangerRick]

The TPS code was for a "Low Voltage" problem, damned if I can remember the actual code.
p.s.
The truck has less than 23k miles.

 

[mjgila1c]

I've been seeing this problem on my Ford Explorer Sport 01 for a while. I've also noticed its a real trend for Fords in general. I've cleaned the MAF sensor and replaced the fuel filter ... no luck. Mechanics have told me that it's caused by contamination on the O2 sensors due to low grade fuel... nothing to be done about it except clean the O2 sensors every no and again.... What is ya'lls opinion???

 

[RangerRick]

I have found that 7 out of 10 times the CEL is caused by a faulty Fuel Pump

 

[slsnut]

Rubber elbow splitting?

Vacuum leaks are a common cause of lean codes on BOTH banks like you are seeing here.

As mentioned above, leaky intake gaskets can be the cause. Although it can happen to any engine, it is especially true on the 4.0L.

Another place to look is the PCV system. A very common problem is a rubber elbow that splits and leaks, causing P0171 and P0174.

I which elbow is this? The 97 Ranger I just bought has an elbow on the drivers side next to the battery that has split and was just off the plastic fitting it goes on. Would this be the one? I just repaired it then went in for smog test. It failed for uncleared codes...
steve