wheels01

So what exactly happens when a check engine light comes on? For example twice now at the track my CEL has come on for a TPS, must have made the wire to short. Now the car still runs but what is the ecu doing with out input from the TPS. Just flooding the engine with fuel? Would like to know.

HondaFanatic708

The TPS delivers a voltage signal to the ECU. At idle (0% throttle) it should be around about .5v The TPS is simply a potentiometer that tells the ECU how open the throttle plate is. At WOT your TPS will deliver a signal voltage of between 4.5-5 volts. If your ECU is throwing a code 7 then there is a malfuntion in the TPS circuit. Most likely and old wire has shorted or prety much broken. I would do some tests on your wiring, I can run you through the process if you are not familiar. You have some of an idea what happens. Lets say your TPS wasn't functioning at all. It would actually be the opposite case. Your ECU would think the vehicle has no load when you may actually be driving at WOT. This voltage signal is used by the ECU to calculate voltage signals to other components such as the injectors. It may only be an intermittent failure which would cause the CEL to trip but it may go back to normal function right afterwards. Either way see WTF is going on with your TPS sensor because it is a rather crucial part of the engines operation and performance...

wheels01

Thanks for the offer. I know exactly what the problem is, and fixed it. Just as you suggested and old wire broke, I tried soldering it, but the wire was old, and the solder made it more brittle but so it broke again. This time I crimped it, should work alot better. What I meant by my question is, what does the ecu do when it isnt getting a paticular sensor, such as TPS. Is there a limp mode were it just uses extra fuel so it wont run lean? It more a question for curiosity sake.

Si Shane

i also have the same question does the ecu add fuel/subtract timing depending on which cell has popped?

HondaFanatic708

In some cases the ECU will divert in to a limp mode. But this only happens when the sensor greatly effects the running capability of the engine or is required for calculating an output. The ECU actually has a ****** mind of it's own. Sensors like the knock sensor, map sensor (sometime can swing), ECT sensor, IAT sensor usually wont cause a limp mode. **** like the IACV will more than likely have some ill effect in performance at some point in the rpm range. It really is a case by case basis. Since a CEL could indicate a problem that was only momentary. You WILL know if your ECU threw itself in to limp mode. If you want more details on the root electronic funtionality I would suggest visiting http://www.pgmfi.org Nothing but good info here.. But if your not a novice at least at electronics you may not understand it all. And I don't mean installing speakers or a stereo, I'm talking circuit design and implementation.

HondaFanatic708

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by wheels01 &raquo;</TD></TR><TR><TD CLASS="quote">Thanks for the offer. I know exactly what the problem is, and fixed it. Just as you suggested and old wire broke, I tried soldering it, but the wire was old, and the solder made it more brittle but so it broke again. This time I crimped it, should work alot better. What I meant by my question is, what does the ecu do when it isnt getting a paticular sensor, such as TPS. Is there a limp mode were it just uses extra fuel so it wont run lean? It more a question for curiosity sake.</TD></TR></TABLE>
If the wire is seriously that bad I would replace the entire length of the wire. From pin to pin. You can use any harness that is underhood. If you go to a u-pull-apart yard you can just clip a few plastic clips from under the hood of really any honda. Use one of those dinky screwdrivers to remove the white plastic shield inside the clip. Then you will see little plastic teeth that hold the pins in. Gently lift this up and gently pull out the corresponding wire. Make sure to save a few cm on the salvage clips so you can solder a new wire on. Repeat the process the remove the junk wire and install the new one. If it wont solder how well do you think it's transfering electricity? Just food for thought..