gear indicator

[jsta6]

I just noticed that Directscan only indicates 3rd or 4th gear.

Is this a directscan thing or an ECM thing? Meaning, was it just not written in to the directscan program, or can the ECM not tell if the car is in 1st or 2nd? (I know DS reads the data before the ECM not after).

 

[TurboDave]

There are only two "gear" switches in the tranny. 3rd, and 4th. The only other things the ECM recognizes is Park/Neutral, or "in gear". If "in gear" and niether 3rd or 4th gear switches is active it assumes 1st or 2nd.

 

[jsta6]

Thanks.

That is good to know.

Today I also noticed that while driving, the "p/n" indicator was on and when I hit 4th gear, the 4th gear indicator did not come on.

 

[Jbenn911]

Sounds like a problem I'm wondering about....no 3rd/4th light up, but the occasional P/N lights up...I've tried cleaning the ECM and DS connectors.. Car shifts and drives fine here...Interested in seeing the replies too !

 

[TurboDave]

The ECM gets its park/neutral signal from tranny linkage running up to the steering column and a switch mounted there. It gets its 3rd, 4th signals from an electrical connection on the side of the tranny which are signalled from withing the tranny via pressure switches.

 

[ijames]

And DS gets its info from the ecm, not from the sensors before the ecm. It reads the sensor values from memory locations in the ecm.

 

[Jbenn911]

(now that i've hijacked this a bit)...So I should check some kind of connector on the side of the tranny ? I can tell on DS what gears are what by the RPM's, just curious if it's a problem not showing on DS(or ECM) even though car shifts ok ???

 

[ijames]

The trans shifts hydraulically, independently of the ecm. The switches are to tell the ecm what the trans did, so the ecm can decide if it wants to lock up the torque converter or pull boost back in 3rd or more in 4th, or add a little timing during highway cruising, etc. Also, the p/n switch tells the ecm which idle speed table to use, and it won't do egr or (I think) charcoal cannister purge in p/n.

 

[Jbenn911]

ok...it does lockup fine while driving, right around 50...but I dont see it on the DS screen , at the track until after I hit the end of the 1/4 and let off the gas, then it lights up..but no 3rd and 4th..any idea what to check on the tranny ?

 

[ijames]

Most street chips don't lock the converter at WOT so it sounds like yours is working as expected. The 3rd and 4th gear switches are normally closed (shorted to ground). The 3rd gear switch opens in 3rd and 4th gears, and the 4th gear switch opens in 4th gear. The connector on the driver's side of the transmission, above the shift linkage, has four wires. The purple wire carries power to the tcc solenoid, the tan/black wire goes from the solenoid to the ecm, the green/white wire goes to the 3rd gear switch, and the light blue to the 4th gear switch. If you unplug the connector from the trans and turn the key on without cranking the engine, direct scan should see both 3rd and 4th gear switches as on (this tests the ecm sensor circuits and the wiring). Also, with engine off both gear switch pins on the trans side of the connector should show a short to the case of the transmission. If unplugging the cable lights the switches and they ohm out as shorted, then either the switch wires are shorted to ground inside the trans pan, or the switches are bad and not opening when they are supposed to.

 

[Jbenn911]

ok...thanks for the explanation!! I'll ask Eric about my chip(TT alky) it's going on the lift later today for a couple things..we'll check it then..i also think i was having an issue with the DS and ECM connectors..appreciate the info