I have a 97 4x4 that just recently stopped shifting into OD. I also noticed that I can no longer switch OD on or off on the end of the gear selector. The litle LED light does not turn on or off. Does anyone know where to start? Just took it on the freeway and the engine sounded like it was working a little harder than normal to be at speed. Confirmed through gas mileage. HELP????

 

take to auto parts store and get codes read. write down and post here.
call ahead at the store, most national chain stores have code reader.

probably related to your vacuum leak.

PCM computer will block out overdrive function with many engine system failures to prevent overloading engine

 

OK, had the engine codes read by Auto Zone. Two codes came out, the first was something new, P0141 which is failure to read the oxygen senson located in front of the Catalyitic converter under the passenger seat. Any comments here for replacing this sensor. Is this a big deal?? The second was one I've had for a while, P1443, having to do with EVAP cannister purge valve mech fault. Any insight on the significance of this error code. Would either of these cause the transmission from shifting into OD.

 

I did replace the main vaccuum hose running from the back of the engine to the brake booster. It was worn down to the cords where it came in contact with the firewall. Also replaced the PCV valve while I had the engine cover off.

 

I'm not sure about the newer vans, especially the 97 model where a single computer controls the engine and transmission. On my 1990 model, I encountered a problem where it would not go into OD because it detected a fault in the ABS. This also flashed an error with the E4WD system, and disabled the cruise control. The original cause was a burned out brake light bulb. Replace bulb, and everything came back normal again.

 

A parts store cannot read your situation. Many transmission shops will read your codes for free. The parts store code readers will not read transmission fault codes and will only read generic trouble codes. You may have a transmission code in addition to the codes you pulled.

The sensor is a pain to change, depending on whether or not it has seized. It is difficult to get a good angle on, and it can take a lot of force to break it free. You can try yourself, but make sure you use the right kind of wrench, a common open end wrench can round off the sensor, a specially made O2 sensor wrench can give you a better bite and you can apply a lot more torque if the sensor wants to fight. If it still doesn't budge, you can try any of the extraction techniques you would use on a normal bolt.

For the record, this is part of why the sensors should be replaced at 80,000 miles. They are maintenance items, and if they are allowed to stay in for too long, they can seize in place and become difficult to remove. If allowed to stay, they can operate int eh grey area, and that can cause clogged EGR passages, excessive fuel consumption, carbon deposits, catalytic converter failure, accelerated engine wear, etc. Better to replace them at 80,000 mile intervals instead of waiting for them to fail.

XLT4WD90, the older vans have a single computer control the trans too. The difference is that the older models only had 2 computer controlled functions and the rest were hydraulic, while the '95 and newer are entirely computer controlled. The '95 and '96 might have a separate computer, but I doubt it.

 

If you have a wrench whose open end fits the HEGO sensor, if it's a combination wrench, use the box end on the sensor body. Usually, the open end should be big enough for the connector to slip through. If not, you can pull the wires out of the connector, and remove it. Once you have the wrench completely around the sensor body, you can apply a lot of torque on it to take it off. A 12 point box end with an angled head should provide a lot of positions that can be used to put over the sensor body.

 

either code will cause the PCM to lockout the OD shift function and keep the van from shifting beyond 3rd and no lockup.

EVAC canister is the plastic box under the air cleaner box. remove air cleaner and replace all the vacuum lines to the canister and purge valve, one long one running back over the engine to a vaccum port on the throttle body, and replace the purge valve MOTORCRAFT Part # CX1158
14 year old rig and too much work and time to remove air box to replace parts multiple times onzy twozy.

 

Going to replace both of them today, The one before the CC and after the CC. The van is up on ramps and if the sensors are a maintenance wear item they should both get replaced. Put some PB Blaster on them and should be able to get off.

Does this code have to be reset of will it go away by itself??????

 

Van has 176K on it and amazes me everyday. Still starts like a champ.

 

OK, replaced with Denso oxygen sensors. I did a hard reset on the PCM by disconnecting the grd on the battery term. Drove the van around for 30 minutes plus highway and idle in a traffic jam and no check engine light. Whats the likelyhood that just replacing the O2 sensors will address my transmission OD issues?

 

Unlikely, since your engine was running pretty decently before. I once had a HEGO sensor fail in the middle of a trip setting the CEL, but it did not affect how the transmission shifted.

 

Whats next? Repaired a main vac hose. Cleared the Check engine light issues. Could the issue be in the switch on the end of the stalk? The shifter lever is pretty wobbly. Maybe there is a chafed wire somewhere? I'm thinking the transmission should shift normally and include OD. The shifts in 1, 2, and 3 seem normal and in the correct rpm range. What about the overdrive drum speed sensor? I'm only throwing this out because I saw it in the top view of the Ford wiring diagram. I have no idea what it does.

 

yes the "clockspring" turning assembly and the rest of the wiring in the steering housing could be shorted and disabling the OD
don't have my Ford CD on this computer so can't help you with exact wiring troubleshooting but look for short in OD switch function.
believe that switch momentarily grounds a PCM lead to toggle force OD on/off. Permanent short to ground would lock out OD.

recheck codes. not all pop the CEL on. Some Ford soft codes will also cause the PCM to go into engine protect mode (LIMP). Ford started this with the mid later 90s models as HP increased to protect the powertrain more completely. The newest CAN PCMs have almost total powertrain protection, i.e. oveheating, too cold, excessive power demands, transmission slippage, bad fuel, ad naseum

 

Here is a thought. I was able to identify the connector from the pigtail of the OD switch. I have the circuit diagram and appears to be a momentary switch to toggle an OD off condition in the PCM. This action also causes the PCM to ground the Led indicator causing the LED to turn on. You have to push the button again to toggle the OD back on again. If something is shorted to ground in the stalk, the PCM doesn't know what to do with this since it is only expecting a momentary switch closure. If I disconnect the connector, it should restore the transmission to normal operation. I just won't be able to lockout the OD function. Does this logic sound correct? Now if it still doesn't go into OD then I'm going to have to take it in somewhere because I'm out of catastrophic events to associate it with.