SOLVED! Persistent P0171 & P0340 and corresponding/related issues:


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Need some input here from you gents concerning the problems I've had coinciding, whilst having both codes. Bear with me, as I might go different directions explaining issues and my thoughts...

Truck has had a high idle and lean issue for a while, that I've sadly procrastinated on troubleshooting properly until now. I think I've had this problem for 4 months? Truck will skip while idling, or at very low speeds. When coming to a stop (usually an abrupt one), the RPM's will kick up to the 900 range while idling. Truck will be skipping when this high idling occurs, 80% of the time. Most times this problem will persist throughout the drive, but will sometimes cease and idle normally on it's own, but with a slight rough idle or hesitation still present. I have noticed that if I drive easy and come to a steady stop I can fight off this problem or prevent it from occurring throughout an entire drive.

It's made me wonder if I got various problems going on, or if this is because of mainly the Camshaft Position Sensor related code P0340. If the sensor is faulty and messing with the timing, would all this be a result??? Wouldn't that also lead to a P0171 code, as the fuel/air mixture would be out of wack due to the Camshaft Position Sensor messing with timing? That makes sense to me, but I could very well be wrong here.

Fuel consumption has ranged from as crappy as 210 miles per tank, to 300 miles per tank (which is almost unheard of for me). Driving behavior has relatively been the same throughout this time, just normal driving without any spirited driving.

Yesterday my Change Engine Oil Light came on, I though this had to be some sort of mistake as I change my oil on September 3rd! Checked the oil today and it's full, but the oil is really dark. Doesn't have an awfully burnt smell though. What would cause my engine oil to get really dark after changing my oil just 3 months ago; actually setting off the change engine oil light? I know that running lean will eventually lead to burnt valves and engine overheating problems... I haven't noticed any overheating symptoms, or even my engine seeming overly warm. Haven't been able to monitor coolant temps and other live date with my phone anymore since my OBD2 dongle stopped working. It no longer sends out a wi-fi signal.

I will be running my laptop and having HP Tuners data-logging a drive tomorrow. I can see what the hell is going on and when exactly. I finally set it all up and registered everything today.

Sorry if I'm all over, kind of typing as I go over this in my head....

I've come up with a to-do list of:
-First off, changing this dark oil out. Oil is still topped off, nothing being burned.
-Do a CASE Relearn with HP Tuners to see if it'll make P0340 go away, hopefully fixing all these problems
-Replace Camshaft Position Sensor, if P0340 returns after successful Relearn
-Check fuel pressure
-Replace Fuel Filter

What's your take on this guys? Again, sorry if I sound like a rambling idiot. My mind is fried and all over the place since I lost my job over 2 weeks ago. I don't have a clear head at the moment. Still haven't found anything... Emissions is due soon as well. I can always remove those to DTC's from ever coming up with HP Tuners, but i'd like them to remain so I can know if I am on the right track to fixing all these issues.


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This link covers the subject matter of the P0171 Trouble Code:

This Video cover the both P0340 and the P0172 Issues:

… and again, this isolated Youtube Video strictly deals with the Tough Diagnostic rundown for the P0171 issue … proving out to be the failure of the SAIS Solenoid located on the Passenger side of the Engine Head... because if it sticks open and allows an excessive amount of air into the Exhaust Stream, when the O2 Sensor picks up the added Oxygen... it signals the PCM to "ADD FUEL" and thus creates conditions where this naturally raises the level of the normal Idle of around 600 RPM to around 900 RPM as a secondary clue that it is a Bad SAIS Solenoid:

If you smell the Motor Oil on the Dipstick and detect excessive Gasoline Fumes... the cause of this problem AND the fact that the Motor Oil is turning Dark or Black prematurely involves one thing: Excessive Blow- By caused by having either Badly Worn Rings in a Very High Mileage Engine… or Stuck Top Compression Rings due to excessive Carbon and Gasoline Residue literally gluing them deep inside of the the Two Top Compression Ring Grooves of the Pistons.

The latter one can be dealt with fairly inexpensively by picking out (3) Sets of Paired Cylinders at a time as one approaches TDC. Then... after removing the (2) related Coil On Plugs and removing the Spark Plugs the Piston approaches Top Dead Center on one of the two matched pairs… with All Four Valves Closed… then fill up the Two Spark Plug Holes with the Canned Liquid Version of ACDelco Top Engine Cleaner until you can see the stuff brimming just above the vacant Spark Plug Hole and beginning to well up inside of the COP Spark Plug Well down inside in the bottom of the Engine Head.

This job will take some time, as you will need to let the stuff sit in there for at least a few hours… or even over night, if possible. The process needs repeating a total of three times for each pair of cylinders that have all of the valves closed when at least one of them is approaching TDC… the Firing Order molded into the top of the Valve Cover will alert you as to which of these (3) pairs line up close enough with one another in the clockwise rotation of the engine. Once all (6) Pistons and Cylinders have been treated… make certain to change your Motor Oil AND Oil Filter... without fail the ACDelco TEC can ruin your PTFE Engine Oil Seals and the lubricity of the Engine Oil as well if left in there for too long.

After performing this treatment... and Before Installing the Spark Plugs... Pull the Fuel Pump Relay and then Stuff some Scott Blue Shop Towels down inside each Paired Spark Plug Wells after completion and turn the engine over for 10-15 Seconds to blow out and soak up of all of that Black Carbon Mung Liquid from the insides of each Cylinder.This will prevent you from accidentally Hydro-Locking the Engine.

You should see signs of immediate improvement in compression... and perhaps this will allow for better combustion and EPA SMOG Test Readings to get you through the Inspection. Changing out your Gas Cap for a Brand New OEM One would also not hurt either and eliminate one less thing for you to have to worry about. Don't forget to replace the Fuel Pump Relay when the work is completed.

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Do one thing here to start. You have a code saying you have a problem with the cam sensor circuit. So try swapping that out. If it doesn't fix it, check the wiring. CASE relearn will do nothing for this as it's not a correlation code.

After fixing that, tackle the lean condition with the usual checks for vacuum leaks, bad SAIS (if you have one), exhaust manifold leak, O2 sensor, fuel and injectors, etc.


Platinum Supporter
Waited a few weeks to post, but the issue was fixed by just replacing Camshaft Position Sensor & Crank Relearn via HPtuners.

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