There was a local repair shop that had an oil change go wrong on a 2011 Kia Optima with a 2.4 L engine (Figure 1). The shop mechanic had an easy task of simply replacing the oil filter and removing and reinstalling a drain plug to drain and refill the engine with oil. The oil filter was installed properly and the correct oil type and quantity was put in the engine but the drain plug was never secured with a wrench and only hand tightened. Somewhere in the thought process the mechanic forgot to tighten the plug with a wrench and allowed the vehicle to go down the road with a loose drain plug.
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Over time and enough road vibration, the drain plug worked its way loose and the oil started to drain from the engine. The driver of the vehicle did notice the oil light come on but proceeded to drive to get to a public destination off the roadway. Some drivers would just pull over, shut the engine off and call for roadside assistance but there are others that will not, and this sealed the fate of this vehicle. The vehicle was driven too far on oil starvation and the engine seized.
Back at the shop
The car was towed back to the shop that serviced it to find out what happened to the vehicle. The shop owner was not a happy camper because he discovered that the drain plug was missing and all the oil drained out leaving behind a seized engine. He confronted his mechanic to educate him about why it is so important to always go over your service repairs and that he would now be partially responsible on some labor involved without pay. Hopefully, this would condition his mechanic to be more aware down the road. To keep operating costs down and not go through insurance, the shop mechanic was instructed to pull the engine so it could be sent to an engine shop for repairs.
Once the engine arrived at the engine shop, they pulled the oil pan to discover a damaged crankshaft and bearings. Luckily the cylinder walls were not scored and most of the damage was lower end. The engine shop recommended a replacement crankshaft, main bearings, rod bearings and an oil pump. The repair shop decided to go ahead with the repairs that would be less costly than purchasing a used engine.
After about 2 weeks, the engine repairs were completed and the repair shop drove there to pick up the engine. Once the engine arrived back at the shop, the mechanic was eager to get the engine back into the vehicle and out of his life. After a full day to install the engine, it fired up and ran. It did not crank over instantly but it did run without any noises or signs of upper engine issues. As the vehicle ran in the bay, the Check Engine light came on, so the mechanic hooked up a scan tool to retrieve any codes to see if he left anything unplugged or not fully seated in the install process.
Whose mistake is it?
The code he pulled was a P0336 for "Crank Position Sensor Circuit Range Performance" (Figure 2). The vehicle never had this issue before so maybe something happened in the engine repair process. The engine was running so the crankshaft sensor had to be working or maybe it had a glitch in it that the ECM did not like because the wiring to the sensor seemed okay. The shop did not have a scope so they were just using old school tactics and a scan tool to figure this issue out. The shop decided to replace the crankshaft sensor with a new one and when this did not work they put blame on the engine shop thinking that they did not set up the valve timing properly.
The repair shop sent the entire vehicle back to the engine shop to have them resolve the issue. The timing chain and gears were checked and everything seemed in order. It was at this point I was called by the engine shop to get a second opinion.
The REAL cause
When I arrived at the shop I was given the whole story of events and I decided the best place to start was to hook up my 8-trace scope and look at the Crank and Cam sensors to make sense of it all. I placed my Yellow lead on the Crank Sensor, Red lead on the Intake Cam Sensor and my Green lead on the Exhaust Cam Sensor (Figure 3).
The signal patterns seemed fine with good signal amplitude and no dropouts (Figure 4) but I needed a good known pattern to compare it to. If you don’t have a good known car to hook up to its always a good idea to head to the Internet to see if you can tap into someone’s waveform library and one great place is IATN if you have a membership to access information. I logged onto their site and sure enough I was able to find a Crank to Intake Cam Correlation waveform (Figure 5). The pattern seemed similar to the vehicle I was working on and the Crank to Intake Cam correlation was identical indicating a non-timing gear issue but what caught my eye was the Crankshaft pattern.