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Throttle Position Sensor


NAXJA Forum User
I have a 1999 XJ sport that throwing a P0123 code. I have replaced the throttle postion sensor 3 times thinking I got defective ones. Still throwing the code, I determined that either the throttle body is really gummed up, (Sprayed some carb cleaner but I think it still needs a good cleaning.)the plug is bad or there's a short on those wires. What is the best method to determine if there is a short, and how difficult would it be to replace the wiring?
How difficult it will be depends on how hacked / perfect you want it to come out. You could go anywhere from a perfect OEM-quality invisible fix that'll take hours to do, to a ten minute "cut the old wiring off and ziptie new wires to the harness from the ECU+TCU to the sensor" hack job.

You'll want a multimeter and a schematic, just find all the connectors the signal passes through and measure at each one till you find the spot where it changes, then inspect the wiring between those connectors till you find the fault.
I had a similar problem and found that the rubber seal on the ecm at the engine harness connector (front connector) was torn. The tear in the seal was allowing water in, causing cross signals and corrosion on the pins and recepticals.
I installed an oring on the outside of the connector, between the the connector and the ecm.
I did this just 2 weeks ago. So far no more problems.
Ill be sure to check the ECM gasket then as well, do you remember which plug it was that on the ECM?