My girlfriend just purchased a 2.5L AT 1996 OBW with 125K miles. I was not able to inspect/drive it before she bought it, so I'm now finding out that the AT Oil Temp light was indicating an issue when she purchased it. It is experiencing the much discussed torque bind and I've become fully versed(thanks to this board) on the diagnostic/repair steps to take with that.

 

Yesterday, on a short day trip the Check Engine Light came on. The code it produced is P0420 - reduced Catalyst Sytem Efficiency.

MY QUESTION: Because the TCU is displaying a trouble code can this cause the ECU to show code P0420 even if the only problem is with the transmission? Should I start with solving the torque binding problem first and see if the CEL goes off?

[...]Yesterday, on a short day trip the Check Engine Light came on. The code it produced is P0420 - reduced Catalyst Sytem Efficiency.

MY QUESTION: Because the TCU is displaying a trouble code can this cause the ECU to show code P0420 even if the only problem is with the transmission? Should I start with solving the torque binding problem first and see if the CEL goes off?

The P0420 code has nothing to do with the trans. That code indicates the ECU "thinks" the catalytic converter isn't performing sufficiently, based on data from the rear oxygen (O2) sensor. That may be the case, or there could be an exhaust leak; in addition, there are some forum members who have found that a defective front O2 sensor can be the cause of that code. At 125K miles, all are possible. Do you know anything about the service history of the car that would allow any of these to be more or less likely?

Do you know anything about the service history of the car that would allow any of these to be more or less likely?

 

Unfortunately, not much. I may try contacting the 2 previous owners to see what they can tell me. The wholesaler she purchased it from had a "once over" done on it and they said the right valve cover gasket is leaky. Would an exhaust leak cause the O2 sensor to trip the CEL? or would that be a different sensor?

 

I was unable to get the "secret handshake" technique to retrieve the codes from the TCU/TCM. Does anyone know the name of the diagnostic tool used to retrieve these codes?

[...]Would an exhaust leak cause the O2 sensor to trip the CEL? or would that be a different sensor?

An exhaust leak that allowed air in before the O2 sensor could cause the problem.

 

 

I was unable to get the "secret handshake" technique to retrieve the codes from the TCU/TCM.[...]

Which "secret handshake" did you try?

Which "secret handshake" did you try?

 

1) Warm up the engine

2) Turn the ignition switch OFF

3) Turn the ignition switch ON

4) Start the engine

5) Drive the vehicle at speeds greater than 12 MPH

6) Stop the vehicle

7) Depress the brake pedal and move the gear selector to "1"

8) Turn the ignition switch to OFF

9) Turn the ignition switch to ON

10) Move the gear selector to "2"

11) Move the gear selector to "1"

12) Move the gear selector to "2"

13) Move the gear selector to "3"

14) Move the gear selector to "D"

 

I think this may apply to newer than 1996 Subarus. I'm thinking I may need to do something additionally with the diagnosis connector and terminals?

[...]I'm thinking I may need to do something additionally with the diagnosis connector and terminals?

See my post #4 in this thread: http://www.ultimatesubaru.org/forum/showthread.php?t=69886

My girlfriend just purchased a 2.5L AT 1996 OBW with 125K miles. I was not able to inspect/drive it before she bought it, so I'm now finding out that the AT Oil Temp light was indicating an issue when she purchased it. It is experiencing the much discussed torque bind and I've become fully versed(thanks to this board) on the diagnostic/repair steps to take with that.

 

Yesterday, on a short day trip the Check Engine Light came on. The code it produced is P0420 - reduced Catalyst Sytem Efficiency.

MY QUESTION: Because the TCU is displaying a trouble code can this cause the ECU to show code P0420 even if the only problem is with the transmission? Should I start with solving the torque binding problem first and see if the CEL goes off?

 

You need an o2 sensor. They only are supposed to last 100,000 miles, but seem to last between 100 and 180K. Odds are its the front sensor, as the rear sesnor tends to have a shelterd life.

This sensor needs to be a OE sensor. The 2nd one can be aftermarket.

 

So how goes the torque bind?

 

nipper

Odds are its the front sensor, as the rear sensor tends to have a shelterd life.

This sensor needs to be a OE sensor. The 2nd one can be aftermarket.

So how goes the torque bind?

 

Well, I've yet to pull the codes from the TCU. I'm going back out today(rain break here in the Puget Sound area) to identify the diagnois connector with a flashlight and a little more patience.

 

Why does the front O2 sensor need to be OE? I assumed the ECU compared values between the front and back O2 sensors and that it would be more important that both sensors were from the same manufacturer.

 

I would like to thank everyone in advance for their assistance.

No no no, the front sensor is the heart of the FI system. The rear one compares with the front one.

Aftermarket sensors can be slow to react, and can cause issues from none, to constantly throwing CEL, to running issues.

 

nbiiper