I got the P0121 last week on my '04 XJR. I'm hoping it was just moisture related, as the car had just sat through a hurricane. We didn't get much of it - the eye went by to the east so we had gusts to 40 or 45mph and some heavy rain. (If it had come ashore south of us I would have left the beach!) Anyway, that was on a Thursday and I had no problems driving 200 miles home that Saturday.

Once I was home I spent about an hour washing the car. I sprayed a LOT of water underneath it to make sure I got any salt. I rinsed the engine, but didn't flood it with water. Saturday evening I went to the store and a couple miles down the road the dash lit up like a Christmas tree with the usual parade of faults across the annunciator. I shut it off for a minute, restarted, and it was fine. I pulled the codes with my WDS and found dozens of faults, including P0121. I cleared most of them (the ones that would clear) and the car was fine the next day.

On Monday I had to drive back to the beach and as the interstate ended and dumped me into Wilmington the car did it again. I pulled off, restarted, and got another hundred yards. I restarted and it was fine after that.

I didn't get a chance to look at it until yesterday, and it happened one more time on Saturday. I pulled the TPS connector, which seemed fairly loose. I reached in with my finger, poked the side of it and it slid apart. I sprayed it with WD40 to displace any moisture, plugged it and replugged it a few times, then put some dilelectric grease in the connector and made sure it was snapped shut. Hopefully that will take care of it.

 

[QUOTE=gmcgann;1015494I pulled the TPS connector, which seemed fairly loose. I reached in with my finger, poked the side of it and it slid apart. I sprayed it with WD40 to displace any moisture, plugged it and replugged it a few times, then put some dilelectric grease in the connector and made sure it was snapped shut. Hopefully that will take care of it.
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Hi gmcgann,

Thanks for the report - I hope you've resolved the issue!

Just for the record, the oily film left behind by WD40 adds electrical resistance to connections, so it may not be the best choice for use on the connectors of many of the more sensitive sensors that provide a variable resistance or voltage to the ECM, such as the TPS, MAFS, O2 sensors, ECTS, IATS, etc. A better choice for those sensors (and most other connectors) would be zero residue electrical contact cleaner, available at most auto parts stores, Walmart, etc.

Using dielectric grease on the plastic connector mating surfaces is a great idea, both for sealing out moisture and to make the connectors easier to disassemble in the future. Some guys apply the grease to the electrical contacts themselves, but that's another practice I'm uncomfortable with since dielectric grease is not only an insulator, but is capable of storing a static electric charge (that's the definition of a dielectric material).

I hope to hear from you that the code has not returned and you resolved the issue by cleaning the TPS connector!

Cheers,

Don