Here we have a 2005 GMC Envoy 4.2 Liter engine. The vehicle is fairly clean and has 112,361 miles on it. The complaint is the MIL Lamp is on and is setting a P0017 code. This code indicates an issue between Crankshaft and Camshaft correlation. The truck runs well and the shop owner was hoping there was a reprogramming that would solve this. A quick check of present calibration and available updated calibrations yielded nothing for this code. Time to roll up the sleeves. First step is to look at the code and more importantly code set criteria. While we are at it check for pertinent TSB's.
Here is the code P0017. I love the code set criteria. A calibrated amount. What is a calibrated amount? Time to dig a bit. I look for TSB's and PI's on the OE site.
I come up with this document. A world of information including the specified calibrated amount as well as a wealth of causes for this code. A little background on these engines. They utilize a camshaft actuator or phaser on the front of the exhaust camshaft that is loaded to a neutral/base position. When the PCM wants to actuate this actuator it duty cycles an oil control solenoid that will in turn feed oil to the actuator and in this case will retard the exhaust camshaft. Basically, this operation takes the place of EGR operation and it also improves overall efficiency. Like all engines that utilize this type of design it is very reliant upon proper oil level, viscosity, and pressure.
Here is the front view of the engine. The oil control solenoid is in the head right by the power steering pump. The camshaft sensor is also on the front of the cylinder head right by the upper radiator hose.
Here is a close up of the oil control solenoid. I see plenty of issues with these. They clog up, the portion inside the head gets clogged up and doesn't allow the oil solenoid to do its job properly. Typically, when this happens the vehicle runs really poor at an idle but runs decent raced up. Think of a vehicle with a stuck open EGR valve. This vehicle runs rather well at an idle. Scantool data is only going to give me a small portion of what I need to know. My play is to scope crank and cam sensors.
Well here is Crank sensor on channel 1 in yellow and Cam sensor on channel 2 in Green. Is it good? Is it bad? I don't know. This is where it is nice to have a known good. It just so happens that there is another similar vehicle on the lot. This vehicle is running fine and is just in for servicing. Lets take a look at that one and see if we can see any differences.
Just a little math here as well. One crankshaft rotation (from signature to signature) took approximately 100ms. That would mean 3.6 degrees per 1ms. The code set was 16.31 degrees which is approximately 4.5ms. Looking at the bad pattern it is real close to being about 4.5ms out. If memory serves me these cam sprockets have 48 teeth that would yield 15 degrees per tooth. So a tooth out with a little stretch is a possibility here as well.