Taurus Speed Sensor

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  #1  
Old 09-15-04, 09:45 AM
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Taurus Speed Sensor

I recently (100 miles back) replaced an O2 sensor on my '94, 3.0L Ford Taurus. The check engine light no longer comes on. I checked for codes anyway and got a constant memory code 452. I believe the constant memory code would only be set in conjunction with a lighted check engine light, since these codes are set while on the road. The other code, 332 is a KOER code.

I am not worried about the 332, since it apparently never happens while I am on the road, and I have already worked this problem. I replaced the sensor, the EGR valve opens, holds vacuum, gets about 15" of vacuum when I rev the engine and the passage is open to the engine, since I get a vacuum leak with the valve removed.

The 452, no data from vehicle speed sensor does bother me. Should it? What does it do? Why does the check engine light not come on if the code is set after I clear the memory? Is this related to the many transmission problems I have had over the last 10 years? Should I fix it?

I tested the wiring harness with the sensor unplugged and the harness disconnected at the firewall. I got continuity to ground on one side as expected from my wiring diagram. I got 26,000 ohms between the two wires and 26,000 between the other wire and ground. Per the wiring diagram, I expected infinite resistance here. Is this the problem?

Any suggestions will be appreciated.
 

Last edited by peabees; 09-15-04 at 09:48 AM. Reason: spelling
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  #2  
Old 09-15-04, 11:21 AM
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speed sensors

are used for many decisions that the PCM must make. it would be helpful if you stated what year, make and model you are working on.

that speed sensor is a pulse generator and has two wires going to it, correct? ok...it generates a ac voltage signal which is converted to digital inside the PCM. putting an ohm meter on the two harness terminals at thr sensor tells you absolutely nothing since the PCM is connected at the other end. you could, however, disconnect the PCM and then check for continuity of each wire but THAT only has limited value. you can test the resistance of the sensor itself and that should be at least several hundred ohms (not sure of the exact spec)...ideally if you did this test at the PCM end of the harness with the PCM disconnected, you would be checking the harness as well. if you get high resistance, then you would go and test at the sensor...resistance ok__wiring problem...resistance still too high__bad sensor.

even better than testing with an ohmmeter would be a digital volt meter set on the ac scale...and even better would be a digital storage lab scope...with that you would be checking all of the critical dimensions of a low voltage input signal.

it's possible that your historical problems may be associated with the speed sensor...but without a detailed history, there's no way to establish a cause and effect relationship
 
  #3  
Old 09-15-04, 12:41 PM
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virginia auto person

Originally Posted by carguyinva
... it would be helpful if you stated what year, make and model you are working on.
see original message

Originally Posted by carguyinva
... putting an ohm meter on the two harness terminals at thr sensor tells you absolutely nothing since the PCM is connected at the other end. you could, however, disconnect the PCM and then check for continuity of each wire
again see original message I was testing the harness. Do I want 26,000 acrooss the wires? The harness was damaged, and I believe the 12v O2 heater wire contacted at least one of the VSS wire and the O2 sensor data wires. I believe I repaired the harness and wanted to know if a resistor was included that would not appear on a wiring diagram. I never lost a fuse so the heater wire did not go to ground(zero resistance would give me battery amps and melt the fuse).

The wiring diagram I got from the Autozone web page shows one wire from the PCM branching to ground on the way to the VSS. The other shows a direct path to the VSS.

MY RESULTS FOR THE HARNESS CHECK:

ONE WIRE, GROUNDED(VSS AND PCM DISONNECTED)

OTHER WIRE, O OHMS FROM ONE END TO THE OTHER(VSS AND PCM DISONNECTED)

OTHER WIRE(AGAIN) 26,000 OHMS TO GROUND

AT PCM CONNECTOR, ONE WIRE TO THE OTHER 26,000 OHMS(VSS AND PCM DISCONNECTED)

AT PCM CONNECTOR, ONE WIRE TO THE OTHER 26,000 OHMS(VSS NOW CONNECTED AND PCM STILL DISCONNECTED)

I think I will run a new wire and see what happens.
 
  #4  
Old 09-15-04, 12:53 PM
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my bad...

...sorry.

no...you don't want 26,000 ohms anywhere.

both wires should have low resistance from the PCM to the sensor.

i don't believe that sensor has ANY grounds in it's circuitry...that diagram you have may be wrong or you may be interpreting it incorrectly...many very low voltage circuits like that are susceptible to induced voltages...so the wires are sometimes wrapped with a drain....the drain wire is NOT part of the operational circuit.

the sensor itself has a resistance of 190-250 ohms

hope this helps...
 
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