Good Afternoon Forum,

Can a crank shaft position sensor fail without triggering a fault code? I have a 2004 Chevy Suburban with 317K that is suffering from the P0300. 145 PSI average cylinder compression with 6% leak down. Everything (coil, injectors, plugs, wires, O2 sensors, evaporator canister solenoid valve, mass air flow sensor) is operating perfectly. I'm left with a crankshaft position sensor and /or cam shaft position sensor as possible culprit yet neither PID's are scanned. Can these sensors fail without triggering a fault code? Thanks for your thoughts!

 

chevy has misfire counters or each cylinder. if you have a scan tool that can monitor live misfire data....use it to determine which cylinder is misfiring.

even if its not setting a misfire dtc for a specific cylinder, you can watch the misfire monitor and determine which cylinder is at fault. post back the results.

-if the misfire is one one specific cylinder...swap a plug, coil and plug wire to a non misfiring cylinder and see if the misfire follows the coil, plug and wire.

-if the misfires are on multiple cylinders...determine if they are all are on one bank...if yes...look at things common to one bank..pre cat 02 sensor.

-if both banks, monitor fuel trim data at idle and 2500 rpm...post results.
using scan tool...determine if misfires occur at idle or off idle by view freeze frame dtc or viewing live data when running.


if you replace a crankshaft position sensor...a crankshaft variation relearn procedure must be done or false misfire dtc will set at high rpms.

evap canister vent solenoid will not cause misfire dtc.

 

Good Afternoon tech 2. Thanks for your prompt response! The moderator changes the title of my post. My actual question is whether a crank shaft position sensor or cam shaft sensor can fail without triggering a fault code on the scanner. I am definitely experiencing P0300 misfires at idle but the engine runs perfectly at 1200 RPM and above.

Given all my replaced parts and diagnostics, the only items left are the sensors but no fault code has been generated. Have you ever heard of these sensors failing without a fault code being revealed? Thanks!

 

Good Afternoon Forum Enthusiats,

Can a crank shaft position sensor fail without triggering a fault code? I have a 2004 Chevy Suburban Z71 (5.3 , Z Flex Fuel engine) with 317K that is suffering from the P0300. 145 PSI average cylinder compression with 6% leak down. Everything (coil, injectors, fuel pump, plugs, wires, O2 sensors, evaporator canister solenoid valve, mass air flow sensor) is operating perfectly. I'm left with a crankshaft position sensor and /or cam shaft position sensor as possible culprits yet neither PID's are scanned. Can these sensors fail without triggering a fault code? Thanks for your thoughts!

 

No. You need less parts replacing , and more diagnosing. Start with suggestions tech2 gave you.
Don't double post please

 

crank sensor causing problems with no dtc: Its possible but rare. I've seen on in 20 years. the fact that the misfires occur at 1200rpm and lower....I would suspect a vacuum leak. check the misfire monitor data, fuel trim % both banks and post the results. Or do the parts cannon then a crank relearn and pray.

 

Dave Hooper

Good Morning,

Thank you! Tech2 suggestions were right on and fully addressed. Parts cannon fired. No vacuum leaks. 145PSI compression with new injectors, plugs, wires and solid 1/2" air spark gap makes this very puzzling. Fuel trims are perfect and the engine runs like a top at 1200 and above. There are only 2 external sensors left that could possibly affect firing - Crankshaft position sensor and camshaft position sensor. No fault codes The engine has recently begun to stall intermittently when slowing down for a stoplight so I'm leaning towards the crankshaft. sensor. I may just as well replace it and pray. Disassembling the engine to inspect the timing chain, camshaft and lifters is the next diagnostic chore on the list but doubtful I will engage given the 20 years and 317K miles on the vehicle. Stay tuned and thanks for your suggestions!

 

what??

that's often a vacuum leak in brake booster

this is usually followed by a complete waste of money.

 

I wish I had a vacuum leak since once identified they are usually easily repaired. Unfortunately, I have no vacuum leaks making this continued misfire point to an internal failure (cam lobes and/or lifters). I don't disagree with the waste of money conclusion but my sense of obligation after 20 years and 317K miles is more emotional than practical at this point. Sometimes one just has to accept the fact that mechanical items fail over time.