So I'm wondering is it necessary to reset the computer after certain fixes, such as, replacing IAC or TPS? Because I had replaced the IAC on my truck and it fixed my idling problem I had. But then the transmission is having a hard time shifting and is holding gears way longer than normal. So I replaced the TPS because I thought that may have gotten damaged, but that did nothing.

Any Thoughts?

 

Yes. Assuming you removed the negative battery lead from the BAT, this automatically resets the PCM. FYI

Anytime you work on the sensors or ANY part of the EFI system, power MUST be removed from PCM input. If NOT- what will happen is, the memory at the PCM level is going to store all that data for motor steps at the IAC, voltage feedback through the range of motion / travel on the TPS etc etc etc.

So, when a sensor is changed out while the PCM memory is alive, it will use data for the OLD sensors that you replaced thus throwing the entire EFI system out of whack. It will not run right until the memory is cleared and all sensors are homed and a NEW baseline is established.

CM

 

Alright, I think I'm understanding correctly. I'll reset the pcm tomorrow morning. Do you have to put in the key and turn it to ON for 30 seconds? or just disconnect the battery's negative terminal?

 

No. You do not. If and when the BAT is out of CKT, ALL power is cut and, regardless of KEY <ON> or not, it's not going to complete the CKT without being tied to ground. It's one of those urban legends / myth busters that comes up from time to time. Another one was to hold the brake pedal for 30 seconds. It's never ending with these kinds of things. Turn the directional on, hold the horn for 30 secs and so on.

As soon as power is removed from the PCM, it takes 30 seconds to fully discharge and drain the caps of stored energy. At that time, the memory and all data is erased. This is also another method used to clear codes by the way. If and whenever you get an OBD FAULT code, to clear it, simply wipe the memory and it's gone- until, the next time it's driven (providing that the root problem has not been resolved).

Another one I don't recommend at all is to SHORT the GND to POS which, can induce failure at the PCM level. While this does work to clear it, it can cause damage to the PCM. The problem is that, when draining the power out in milli or micro seconds, it is hard on the caps to go from a fully charged state to 100% discharge in a fraction of a second. The internals of those caps can't handle that kind of abuse and, if done repeatedly or, it's a weak cap to begin with, it will either break down and fail to hold charge or, it won't work to full capacity to where, it will not hold a full charge thus, it will fail to provide the proper voltage to the rest of the circuit. Worse case, the cap will short. It should also be noted that a voltage spike due to this shorting at the battery leads can lead to either latent or catastrophic failures of voltage sensitive components inside the PCM.

There is a way to use this method safely and reliably by implementing a shunt to ground. Both methods will work in your case. Just remove ground for 30 seconds.

NOTE: BEFORE CONNECTING THE NEGATIVE LEAD AT THE BAT: verify that all CKTS (circuits) are OFF, radio is OFF, all doors are CLOSED, all LIGHTS are OFF etc etc. WHY DO I HAVE TO DO THIS? If there's a CKT on such as the headlamps / lights when connecting the NEG cable, it will ARC or spark causing a voltage spike that is very damaging to diodes, filter caps and voltage sensitive components.


Hope that helps,

CM

 

Awesome, Thanks for the help man I appreciate it.