I have a 91 f150 4x4 with the e4od. From what I can tell the tranny is in limp or safe mode. It only opperates in 2nd and 3rd gears by manually shifting from 2 to drive. Will not go into first when shifted to 1. Od does not engage. The od off button don't light up when pushed. I have replaced the solenoid pack, the throttle position sensor (don't remember what it's really called), and replace the ecm with a used one from the bone yard (the original ecm did have a broke capacitor and the others were corroded badly). I checked all the fuses. I looked and cleaned the speed sensor in the rear diff. The koeo test only shows codes 67 and 52. I know that 67 is park/neutral switch fault and 52 is power steering switch open. Will the park/neutral fault cause the limp mode and I should replace the mlsp or is it something else? I have read through all the forums I can find and not any of them mention those codes. I can't even get the koer test to work. Even checked it at the local parts store with their scanner and they showed the same codes for koeo but they couldn't pull any koer codes. Another thing I checked was the line voltage to the solenoid pack it seems that there are two wires at the back that have power (the last two wires at the end of the plug toward the rear of the tranny). I do appreciate any help I can get. Please, let me know if more info is needed. I'll check back in the mornin. Thanks.

 

You're not getting power to the shift solenoids. This is probably a wiring problem. I don't have a wiring diagram for your truck, you need to find the two pins that should have +12 at the right hand side transmission connector and find out what's wrong with that circuit.

 

That was one of the things I looked into and I found two wires have power but didn't do anymore testing. I will look into it more.

 

Ok, here is where I am at. I pulled the wire harness out from the tranny to check for bad wires. It has continuity from all three plugs (white, green, black), back to all the plugs around the tranny (mlps, solenoid pack, transfer case, speedo plug). I have voltage at the red and the white wires going to the solenoid pack. I did clean all the connectors and connections. I'm goin to replace the mlps, I believe it to be the original grayish tan switch. Then next it will be the speed sensor in the rear diff. Is there anything else I need to look into? Thanks.

 

I do not see why you are replacing the MLPS (TR sensor) or the Speed sensor (VSS).

The plug for solenoid pack is more than likely your problem. Pull the back of the plug apart and see if the wires are bad going into the plug.



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I failed to mention that I will be replacing the plug for the solenoid pack that is the first on the to do list there were a couple of wires with the insulation coming off at the plug. However, everything tested good from one plug end through the other. I have read that the pin holes to the pack may be stretched or expanded and most likely not making connection. I was wanting to know if there was anything else I could run in to. I like having options and knowledge. Thanks.

 

Thanks for the diagram this will help. The Haynes only goes so far.

 

Finally got the solenoid plug replaced. Reset the ecm. It is still in limp mode. The next on the list is the mlps, then the vss. Is there anythin else I'm missing?

 

That's not going to fix it. You need to troubleshoot for broken wires or a bad solenoid.

 

Not sure what the replacing the MLPS (TR sensor) will do for you but the VSS will not cause limp mode. The VSS can cause harsh hard shifts (high oil pressure) but you should have all of the gears. If you have a VSS problem you will get a code in CM but it will not turn on the MIL.

 

In case you have not read the following about LIMP mode here is some reading for you:

"Limp Mode" or "Fail Code" Condition
"Fail Code" conditions or "Limp Mode" happens when the vehicle computer recognizes a problem in it's logic. When an expected signal value from a sensor is sent to the computer and is not within the computer's programmed specifications, "secondary" programs are activated by the computer to strive to protect the transmission from damage the improper sensor signal might cause to occur.

In other words, the computer is always expecting certain signal values from certain sensors i.e. the temperature sensor, the speed sensor, the throttle position sensor, etc. As long as these signals are what it would normally expect for the conditions and is normal based on all the other signals it is receiving from other sensors, it acts normally and accordingly.

If the computer, all of a sudden, receives some crazy signal from one of the sensors that is out of the normal range expected from this sensor, it will go to "emergency" or "secondary" measures.

These emergency measures vary depending on the severity of the defective signal. All this is preprogrammed into the computer's logic by the manufacturer. The manufacturer has decided that as long as a certain parameter of a particular signal is sent from a sensor to the computer, all is well. The manufacturer decided that if this signal is higher than their highest parameter or lower than their lowest parameter, something is wrong with that sensor and the computer should make someone aware of the situation and take action to try to "save" the vehicle systems or powertrain.

Perhaps the computer will simply cause the "check engine" light to come on. The signal variation wasn't severe or critical to cause any mechanical failures but the vehicle's operator is made aware that he or she should have the vehicle checked out electronically to see if a minor sensor has broken down or is starting to send the odd irratic signal. This type of condition is commonly referred to as a "soft code". Normal functions are not affected but if the repair is not made, performance or fuel efficiencies might suffer. Perhaps the sensor only malfunctioned one time and all other times was fine. This might be an early warning of a sensor that is beginning to fail or has a loose connector or connection.

Other times the signal needed to perform operations normally is so far out of specification that the computer has no choice but to go into survival mode. With transmissions, the computer will cause the internal tranny fluid line pressure to default to high to protect clutches and bands. The transmission also turns off the shift solenoids to cause the unit to default to a single gear, usually second or third. All normal instructions to control line pressure are overridden so a hazardous "slipping condition" cannot occur easily. This theoretically is so that the vehicle's driver can get the damaged vehicle to the next town for repairs. This condition is commonly called "Limp Mode" for this reason. You limp to the next town in second or third gear only, at full line pressure so the tranny guts won't slip on your trip in.

By the way, interestingly and just as a side note, if the cable harness going to your transmission was ever to become detached, severed or damaged, your transmission would also go to "limp mode".


The vehicle's computer would immediately sense that it has lost contact with the transmission and would set the codes and send "limp mode" signals to the tranny. But because the harness is severed between the computer and the transmission, no computer signals will reach the transmission. These sent signals, however, would have had the identical affect on the transmission as what taking away supplied power to the shift and line pressure solenoids has as in the case of a transmission harness being detached or cut. Due to the engineered voltage strategies of the solenoids, the transmission simply defaults to a single gear and line pressure defaults to high, all in order to "limp" you home.

A Throttle Position Sensor that improperly sends a reading that it is wide open when in fact it is physically closed would be detected by the computer when it compared this reading with the vehicle speed sensor that perhaps is showing very slow vehicle speed. The signal, by itself can't be considered wrong but when put against all the other sensor signals of the system might cause a computer concern. The computer, at this point, unable to "trust" the collection of signals because together they are not making sense in it's logic, will simply go to limp mode in the transmission to protect it and make the operator aware that something is wrong with one of the sensors and a mechanic's attention is needed to correct the situation.

This Fail Code Condition will show up as a "code" reading on a mechanic's scanner. This code will be cross referenced to a table from the manufacturer and represent a problem with a particular sensor or a group of sensors or system. It gives the mechanic a better idea of where the problem has showed up and which systems or sensors are involved in the malfunction. The table of codes and what each one means, is commonly programmed right into the scanner tool that the mechanic uses for easy reference.
i.e. the scanner tool might tell the mechanic that the computer has thrown a code "35" which is the "transmission fluid temperature sensor" and might give the mechanic the recommended values this sensor should provide and what it in fact provided...

In your electronic transmission, many important functions are controlled by the computer. Shift timing, sequence, feel, line pressure are controlled. The information from the vehicle speed sensor affects fuel injection, fuel mixture, ABS, transmission operation, etc. Load information of your engine is commonly taken primarily from the TPS (throttle position sensor) or the MAP sensor (manifold absolute pressure). This controls transmission shifting and downshifting when stepping on the gas or climbing hills. A regular scanning of the computer for any set "hard" or "soft" codes is something routinely done by most good tuneup shops these days.

 

Solenoid has been replaced. All the wires from the trans harness tested for continuity between the three plugs on the fender well through all the plugs including the new solenoid plug, mlps, transfer case and Speedo sensor. There is power to the solenoid pack via the red and white wires although I am unable to confirm the actual voltage at this time (do to using an old analogue volt meter). Thanks.

 

I've pulled 3 codes. 67, 52 and 11. 52 is power steering pressure switch is open. 11 is ecm functionin properly. Now 67 is park neutral fault. That is what leads me to believe that the mlps is bad. This is the second ecm but throwin the same codes.

 

67 usually means that the heater or AC was in the on position during the test.
52 usually means that the steering wheel was not turned during the test.
11 means that that there were no codes in CM. Cm is where the VSS code would have been if the battery has not been disconnected.
I am guessing you did not run a KOER self-test.

 

Ok thanks for clarify. I was goin by what I've read online. So, the codes don't really tell me anythin helpful. Btw, I can pull codes from koeo but not with koer. Not even with a scanner. The check engine light is not on but does work for the codes. The only lights that are on is the brake and abs.