code 28 what do i do!!! vs auto transmission oil pressure

[SKNOT9]

as the title states. What is wrong with my car? engine light came on and i have no idea what is wrong or what to do to fix it!! please help!

[hq-racing]

first thing i would look at is, is there ne fluid in the trans...
it might have just got to hot, mine use to do the same thing when left in werid positions, just have to turn it off and start it again..

[immortality]

yep, check fluid level first. if it's fine then possibly the oil pressure sensor in the trans may be stuffed (the ecu on 4L60E equiped cars controls the line pressure in the trans) or you may have a wiring problem so also check the connector plug for the trans and make sure you don't have any damaged wiring

[SKNOT9]

thanks for the help guys, checked fluid level and took a bit out as it wus just over full and engine light has gone away.

[Cheap6]

Probably is the fluid pressure switch assembly and the light will come back. That's a large - ~100mm X 200mm - black chunk of plastic bolted to the valve body inside the auto. pan. The switches are inside that.

There are three wires from the switch assembly to the PCM for the switches and two for the temp. sensor (= 5 in total). The ones for the switches are the important ones. Each of the three wires is earthed by various combinations of 5 switches inside the switch assembly actuated by the presence or absence of fluid pressure. The combined output at the PCM is all you need to check though.


With a voltmeter or test light, at the PCM, back probe (using a pin in the back of the socket to each of the PCM terminals) between each of the three wires to earth, engine running:

Terminal B4 - tan wire

Terminal B3 - yellow

Terminal B2 - green/yellow trace

Gear Selector position. At B4. At B3. At B2.
Park: 12V 0V 12V
Reverse: 0V 0V 12V
Neutral: 12V 0V 12V
D: 12V 0V 0V
3: 12V 12V 0V
2: 12V 12V 12V
1: 0V 12 12
Not valid: 0V 12V 0V
Not valid: 0V 0v 0V

(0V means that the switch combination is closed, 12V = open.)

If the results don't match the tabled values, then you can move further down the wiring circuit from the PCM to that connector plug on the LHS side of the trans. (as per immortality ^) then into the trans. I think that the switch assembly is the most likely suspect though. It's easy to replace, only needing the pan to be removed for access.