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I have 1996 Acura 2.5 TL ( 5 Cyl.) with 90k miles. Auto trans
My scanner shows an intermittent VSS signal or reading on the ECU. Most times while driving VSS reads 0 mph on my scanner while driving but will occasionally read correct speed or a lesser incorrect speed. When vss reads 0 while driving then my timing stays static and reads 7 degrees. When the VSS reads a speed on the scanner, the engine timing changes and the car runs better for,that short period of time until the VSS goes back to reading 0.
The OBDII also shows the short term fuel trim running at -20 and I get Misfire DTC’s at above 4000 rpm. (random Cyl. Misfire or a specific Cyl Misfire typically Cyl 1 or 2).
Transmission also shifts improperly by staying in gear until high RPM’s are reached before shifting unless you left off the gas a bit to cause it to upshift.
The car has mechanical VSS (vehicle speed sensor) that is driven off of the differential and a new unit was installed but made no difference in performance. The VSS is a 3 wire unit (ground wire, 12 v from ignition and output signal wire using a Hall effect style sensor with a spinning magnet). The output signal goes to the speedometer/odometer, the engine computer (ECU), the transmission computer (TCM) and the electronic cruise control unit.
My speedometer works fine as does the cruse control. I don’t have any error/DTC codes for the VSS in the ECU or the TCM but as I have siad, the VSS reads 0 mph on my scanner most times when driving.
The VSS puts out an alternating electric pulse when ignition switch is in on position ( not running), car in nuetral and the wheel is spun by hand when left wheel is jacked up. The voltage oscillates from 100 mVolts to 9.3 +/- volts. factory manual states it should oscillate between 0 & 5 volts or MORE. I also get this voltage measuring at the ECU electrical plug and at at the TCM plug.
Is this VSS output voltage too high? Should it actually got o zero vs the 100 mVolts i’m Reading?
I have TESTED AND i’m Getting 12 volts at the VSS plus with ignition on. I get oscillating voltage output from the VSS wire at a wiring harness connection under the hose as well at the ECU and TCM connector plugs (same voltage readings at each location). (Note: I did not test voltage at Cruise control unit as it is not easily accessed.)
I have continuity between the VSS orange wire at the ECU plug and the VSS orange wire at the TCM plug.
if I disconnect the 3 wire plug from from the VSS and drive the car, I get a transmission error code but no ECU error/DTC code.
Does anybody have any suggestions or know what maybe causing this? Any help,is appreciated.
Note: I have factory service manual and wiring diagrams from All_Data. I do not have factory wiring diagrams.
I have been following VSS test procedures from,factory manual but to no avail.
Have you tried reading voltage at ORN wire with the 3 pin VSS connector while disconnected? You should have a 5 vref on that wire from ECM with plug disconnected.
The hall-effect sensor should produce a 0 to 5 volt square wave signal with wheels spinning. Hz should increase proportional to wheel speed. 9.3V is way too high.
The enable criteria to trigger a VSS DTC on EARLY Honda/Acuras is 5 seconds or longer/ <4000RPM. The signal has to be completely dead to set a code. In your case the ECM is seeing a close to zero (100mV) and a 9.3V back and forth activity. It just doesn't have the capability or "teaching" to see anything wrong and will not set a code.
