Just for the heck of it I checked my ECU and TCU (Transmission Control Unit) codes a few days ago and got 0504 and 0304. I then reset both the ECU and TCU. When I checked again last night the same codes were there again (why am I not surprised)


This is what I got a week ago and again last night:

ECU:
0504 - Automatic Transmission Control Unit Signal to ECU
0304 - Knock Sensor

TCU:
3rd flash longer than others = Throttle sensor circuit is shorted or
disconnected


Could a bad Throttle Position Sensor (TPS) be causing all three codes? This is what I think:

TPS sends signals to both ECU and TCU. If it's bad and it fails to send a proper signal to TCU that could cause ECU to display the 0504 code. Since the TPS is also not sending the signal about correct position of the throttle plate to the ECU, the ECU cannot adjust the air/fuel mixture properly and therefore the 0304.

I will check the stupid TPS tonight when I get home.
In the meantime, please tell me if I may have something here or am I just talking nonsense.


Thanks.

 

Your reasoning sounds excellent. Do you have a Haynes shop manual? There are two pulgs on the TPS, two unique settings you can check. I think one is for throttle open or closed (basically a switch) and the other is the TPS variable signal to the ECU. You can check them both, the Haynes manual tells you how thats done.

One a side note, my 99 threw 0504 when it was under warranty. My dealer had to order new controllers for my car. It drove perfect aside from the CEL light that popped on. Hopefully that isn't your problem, I did not get the infamous 0304 code along with it.

Keep in mind, the 0304 can be coming from something else as well. You may have excessive ping or knock which the sensor is recording, thus setting that flag in the ECU. It might be the TPS, then again it might not.

Let us know how you make out with your testing of the TPS. If you need the instructions, PM me and I'll get them from the Haynes book for you.

 

Thanks njmaxseltd. You are one of the .org memebers that never fail to help when they can. I am grateful for that.

I do have Haynes and I found the section with the TPS check and adjustment but I haven't had time to read it last night. I'll check it out tonight.

My CEL is not on and I just checked the codes because I thought shifting was funky. When I reset the ECU the car drove and shifted much, much better.
I just hope I don't have to replace both TPS and KS. I don't even want to think about TCM.

 

Update:

My TPS checks within specs according to Haynes. I still get the "Throttle sensor circuit is shorted or disconnected" on the Transmission Control Module.
My KS is dead (open circuit) but I don't think a dead KS can affect TPS in any way.
It must be either a dead Transmission Control Module or the connection to it from the TPS.

Question:
Where the is the TCM located? I can't find it in Haynes.

 

Are you sure the KS is dead? They are supposed to measure very high resistance, almost open. What setting was your OHM meter on or how high is it capable of reading?

ECU/TCU I believe is all in the same unit. Somebody correct me if I'm wrong. Thats why guys swap the ECU when they do a 5 speed conversion. When Nissan replaced mine, under warranty thank god, they needed my keys to reprogram, that alone tells me the ECU/TCU is one in the same.

 

I measured the KS resistance with two different digital multimeters - a $20 one and another $150 professional multimeter (idiot proof plug and play) - just to be sure.
I also thought that the TCM was a component inside the ECU, but I heard someone say it may be in the dash behind the glove box (which I thought was not true).

 

I have the 0504 code as well, and TCU code comes up as a short 2 and it came up as a bad speedometer sensor... Called a local tranny shop and they have no idea what the code means, has anyone seen this code, or had a similar problem?