Over the past year, I have had an intermittent CEL 0104 (vehicle speed sensor), along with 0504 (a/t control) and 0304 (knock sensor). The speed sensor checked out, plus my speedometer was functional. My guess was that the signal path from the speedo head to the ECM was intermittent. I was able to borrow a portable o-scope and monitor pin
29 (vehicle speed sensor) of the ECM. The signal during normal operation was a 0-10V square wave where the freq would vary with vehicle speed. A few times the signal would be stuck at 10V or 0V. When this would happen, the CEL would trigger. I banged on the dash near the speedometer and the square wave returned. I later took the dash apart and cleaned the connections to the speedo head with contact cleaner. I continued to monitor pin 29 and for about a month now the signal has behaved normally and no CEL.A few days ago I checked for non-CEL DTC's. I had both 0504 and 0304. The FSM continutity test of the 5 wires to/from the ECM and A/T control unit passed. The short to ground test also passed. The FSM is vague on any more detail on the specific function of these 5 signal lines, so although I could monitor them, I'm not sure what to look for.
I've also been monitoring pin 64 (knock sensor), it's voltage varies from 2V to 3.3V. Is this normal operation for this sensor? I was expecting the voltage to increase if I accelerated hard, but have not yet noticed a consistent pattern.
Part of my impetus for checking for DTC's was that I noticed a slight hard shift from 1st to 2nd.
Appreciate any helpful thoughts anyone might have.
I use premium gas, usually Shell 93. 159K miles. Maxima SE.