Earlier this year, I replaced/upgraded the following components.

• Replaced power steering pump
• Deleted faulty power steering idle-up valve
• Replaced leaky power steering pressure hose
• Replaced faulty camshaft position sensor
• Replaced coolant temperature sensor (preventative)
• Installed 320A alternator and 1/0 power/ground cables
• Installed 1/0 negative battery cable (big thanks to YODAONE for the comprehensive write-up!)
• Installed shorter serpentine belt
• Replaced the trunk seal

Since then, I have been having this intermittent check engine light for the knock sensors (usually Bank 1). The strange thing is I had both replaced in October last year with brand new OEM parts during my starter replacement. From what I can tell, it only seems to happen following instances of hard/sustained driving - think long highway cruises, or maybe spiritedly driving through the city - hardly a regular occurrence at that. My check engine light will turn on, and the car will enter a "limp mode" of sorts. Acceleration is poor, and the transmission's shift points are kind of all over the place, while the shifting itself is pretty hard. Strangely, the issue seems to remedy itself after I let the car sit for a couple hours. If the light doesn't go out immediately, then the car will be out of "limp mode" and the light will clear itself a day or two later.

Personally, I'm kind of stumped, as I know I replaced the sensors, so the issue shouldn't lie there. If one or both of the sensors were faulty, then I feel like the problem would be more consistent. My mechanic friend thinks it might just be a side effect of the higher output alternator, and another friend recommended that I look into replacing my spark plugs.

Has anyone experienced a similar issue, or have any ideas of what to check? It's not really a detrimental issue to me, but it's just disheartening when a lot of time/money goes into maintenance, only for the car to find new ways to act up.

 

did u replace the harness/connectors when u replaced the sensors? what brand of knock sensors did u use? knock sensors are fragile..shouldnt be dropped.

 

Check the resistance at the ECU side. The parallel resistance will tell the connection issue. The ECU connector A pin#17=Knock Sensor R, pin#18=Knock Sensor L. The common ground is the pin#21 and 31. I don't remember the value exactly but it was around 200kohms.

The knock sensor itself is a ceramic transducer/microphone and the resistance is infinity but a parallel resistor is installed to reduce the impedance aiming to improve the S/N ratio and also to make it possible to check the connectivity check. The ECU checks the static resistance and judges that the sensor is connected or not.

Another smart idea to check the sensor is to use an oscilloscope. You can get the signal 1.0Vp-p max when the knocking is not happening. When it is happening, the amplitude is more than 2.5Vp-p.

 

The harness/connectors are still original. The knock sensors were Denso #89615-12040 and to the best of my knowledge, they haven't been dropped by me or my friend who installed them.

Thanks Yamae, I appreciate your technical input! I'll try and see what I can do for checking the resistance

 

should have changed the connectors/harnesses