92 LX - Codes 67 and 79 - Need some help please

[Hi-Po]

I did a KOEO scan today and came up with two a/c related codes - 67 and 79

According to the scanner:

Code 67 - A/C on during KOEO or neutral drive switch open or manual lever position sensor out of range or neutral pressure switch closed or Park / Neutral switch open.

Code 79 - A/C or defrost on during KOEO test.


The car is a manual. I have disconnected the wires from the a/c compressor a while ago as the compressor seemed to be working even when a/c was switched off...

I know nothing about air condition systems, so any input as to what may be wrong or any tests I can perform would be greatly appreciated!

 

[jrichker]

Code 67 - clutch not depressed (5 speed) or car not in neutral or park (auto) or A/C in On position
when codes where dumped. Possible neutral safety switch or wiring problem. This code may prevent you
from running the Key On Engine On tests. You can generally ignore this code, since it has no effect on
engine performance.

The computer wants to make sure the A/C is off due to the added load on the engine for the engine
running tests. It also checks to see that the transmission is in Neutral and the clutch depressed (T5, T56,
Tremec 3550 & TKO)). This prevents the diagnostics from being run when the car is driven. Key On Engine
Running test mode takes the throttle control away from the driver for several tests. This could prove
hazardous if the computer was jumpered into test mode and then driven.

The NSS code 67 can be bypassed for testing. You will need to temporarily ground computer pin 30 to the
chassis. Computer pin 30 uses a Lt blue/yellow wire. Remove the passenger side kick panel and then
remove the plastic cover from the computer wiring connector. Use a safety pin to probe the connector
from the rear. Jumper the safety pin to the ground near the computer.
Be sure to remove the jumper BEFORE attempting to drive the car!!!

Code 79 - A/C is on, or computer pin 10 is shorted to power.

See the diagram below and you will find the very first wire starting from the bottom of the computer
connector is a pink/lt blue wire that connects to pin 10. Disconnect all the items plugged into the pink/lt blue
wire like the pressure cutout switch and the A/C defrost switch. Look for the 12 volts to go away when the
pressure cutout switch and the A/C defrost are disconnected. If they don't, the WOT relay wiring may be
bad. The WOT relay is located on the inner wheel well under the Mass Air meter.

Diagram courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)
for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should
bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

 

[Hi-Po]

Great info jrichker, that was very helpful!

I'll try to bypass the code 67 tomorrow as per your advice, as I tried to do a KOER test after the KOEO test but the scanner I used (Autoxray CodeScout 2500) couldn't read any signals with the engine running.