mjm4jc

Greetings everyone,
I was suspecting that my TPS harness (with the two light bulbs) that I use to set it wasn't working properly. I could get no lights and just one light, but never could get two lights. So I made another harness, since the old one was frayed and corroded. Same results with the new harness. I know that having just one light means it's within range, but I find it odd that I can never get both lights to come on no matter how much I take the plunger in or out. Just wondering if this could be a sign of a failing tps? BTW, this is for my gsl-se.
Thanks!

LongDuck

Possibly - are you sure your bulbs are good? I use old filament bulbs soldered together for sheer simplicity vs. LEDs, and the FSM covers this using 2 voltmeters (meh.). If your bulbs are tested good (12v - straight off the battery), and you can only ever get one lit, then I'd say it's probably one of the bad switching solenoids - not necessarily the Throttle Position Sensor, itself.

Recall that the TPS is nothing more than a carbon sheet attached to the plunger arm with a spring to return it to the idle position. As the throttle moves, the carbon sheet moves under the 2 contacts, changing the resistance as read out to the ECU. From there, the switching solenoids are operated to activate your test bulb fixture. If one of the switching solenoids isn't working, you won't get 12v power to the bulb. The solenoids in question are the 2 round brass-colored 'barrels' in the rat's nest which are wired together with a common lead and 2 separate power leads.

You probably already know this, but the bulb test to set TPS is done with engine off but previously warmed up. Mine seems to have the best throttle response when the 2nd bulb is *just barely* out, and even looking at the throttle rod sideways allows it to turn on. This way, your ECU knows when just off-idle occurs and starts the acceleration map for timing and fuel injector pulse. YMMV (literally, on this one...)

mjm4jc

Excellent response LD. I wasn't even thinking about the switching solenoids. Good insight. Both bulbs are good for sure, as I swapped them and got the one light to come on with the other bulb.

I find it interesting to set it at the threshold of both lights coming on. I'm assuming this would be closer to the 1500Kohm range? Previously, I had it the opposite direction and barely at 1kohm. It does idle extremely rich.
I will check the solenoids. Thanks again.