Almost didn’t get home with my 1994 F-150.
It is a 5.0 with E4OD,4x4 and has about 179,000 miles.. Could not get over 20mph and the transmission was slipping a lot.

Bought a OBD1 reader and the KOEO codes were 172,334, and 452.

172 HEGO (HO2S) sensor fault/lean
334 EGR closed valve voltage high
452 Vehicle Speed Sensor (VSS) signal fault.

I have no idea what these things are,or where they are. Do I start replacing things? The book that came with the reader indicated these items need to be fixed before additional tests are done. Any help will be appreciated !

 

Yes, you need to resolve any KOEO codes before the KOER test can be performed.

Given that you're having difficulty with vehicle speed, I'd say the VSS code is where you want to start.

Since the code is defined as a SIGNAL FAULT, you need to check the wiring related to the sensor. This includes continuity and checking to see if the computer is actually receiving the signal from the VSS. The VSS is located on the transmission, however, I can't say for sure where so someone else will have to supply that info.

You'll need a multi-meter, digital or analog, to check the wiring. If you've never done this before, get a digital meter as it will be easier for you to operate and read. A cheap one is around $20. I'd also advise you to buy alligator clips for it as well, as that will make this much easier.

To check continuity, you need to read the resistance of the wire. As a reference for what you should see for a resistance, touch the test leads together before checking the wire. If, for example, your meter reads 0.9 ohms, then you'll be looking for about 0.9 ohms when you check the wire, give or take 0.2 ohms. If there's a drastic difference, there's definitely a short, most likely an exposed wire that's grounding out.

So to actually check resistance, you'll clip one test lead onto the VSS end of the wire, and using the other test lead, touch the wire where it hooks into the computer. It's located in driver side corner of the engine bay on the firewall. It's a big black connector, and you might have to remove a couple of things to reach it and remove it. Make sure the NEGATIVE battery cable is unhooked for this process. Once it's removed, you'll insert the test lead from your meter into the correct pin on the connector. (I'm sorry but I don't have the information needed to give you specifics on which pin you need to check. Go to Fuel Injection Technical Library and you should be able to find some of this info.) As I said, if you're reading close to the resistance (ohms) as you were when you touched the meter test leads together, then you have good continuity.

The next check is to see if the computer is actually receiving the signal.

So basically you want to hook everything back up to check if the computer is receiving the signal.

If possible, with KOEO, check the DC voltage output of the VSS on the return signal pin. To be honest I don't know what it should be or if it puts out a voltage reading, but if it does, all you're looking for is a reading to use as a reference. Once you have that, you can hook the sensor back up and check the voltage reading at the computer.

This is going to be a pain, because in order to see what the computer is receiving from the VSS, it has to be hooked up. This means that you can either try to back probe the wire in the harness, or you can release the wire from the harness by partially disassembling it and releasing it using a small screwdriver.

I think that's everything I can tell you. Obviously, keep us updated and ask questions as you need to know info, and we'll help you figure this out.

 

I have never had this happen in my Fords, but I did own a Jeep Grand Cherokee a few years ago, that when the O2 sensed a lean condition, would put the vehicle in "Limp" mode, in which the transmission would only stay in 3rd gear, would not shift and felt like it was slipping a lot, when the O2 sensor threw the code, it also threw a speed sensor code, so you might want to do some checking to see if the Fords have a limp condition if that O2 sensor goes out.

 

Thanks guys. The O2 sensor was replaced about 4000 miles ago as well as the plugs, but I guess it can go bad quick. I will get a digital meter and check the wiring.

 

Yes, the O2 sensors, especially the earlier year models can go out very quick, I have seen them go from newly installed to dead in 2 weeks and less than 500 miles of driving.

 

Barring faulty manufacturing, the only thing that can ruin an O2 sensor in that short of time is:

1) Improper installation (meaning it doesn't stay tightly threaded or the flutes have oily/greasy residue from being touched)
2) An extremely rich running condition
3) Bad piston rings that allow excessive oil blow by and therefore, excessive oil in the exhaust and coats the sensor, similar as in a rich running condition.

There may be a few other things I'm not aware of that cause such a failure, but an otherwise good sensor should function for about 50,000 miles depending on your driving habits.

I'm not saying don't check the o2 sensor, since that can certainly be a possibility, but you definitely want to make sure the wiring to and from the VSS is solid.

 

Well, you nailed it on the head there DBG, I said, they can go bad very fast, I didn't state any of the causes, but the symptoms could be indicative of that sensor going bad, if there is a limp mode situation. If that sensor has gone bad, then further investigation into why it went bad is in order.

The guy asked a question, I offered information based on my over 40 years of driving experience. I would definitely check all three of the codes and what their causes as well as solutions are.

 

I understand. The OP appears to be a noob and I just want to do my part to make sure he's getting as much complete information as possible. One of the things that frustrates me, not just when I first started wrenching but even to this day, is when I don't have enough information. You can tell me that a sensor went bad after 2 weeks and I will wonder why until I have the answer. But that's just me.

 

In a Ford truck a dead O2 sensor will not cause the level of problems the OP is seeing, that VSS problem will however as it is a critical computer input for transmission operation.

 

Thanks everyone. It was the VSS/ABS sensor. I replaced it, disconnected /reconnected the battery, problem solved. Evidently the sensor set off a chain of events that generated the other codes.

 

No it did not set off codes for a lean condition or EGR feedback fault. It's a matter of time before codes 172 and 334 return.

Glad to see you did resolve the driveability issue!

 

I'm having an issue with a couple of those codes as well. I have a '95 F150 4X4 w/5.0L automatic.
My truck runs and drives well, (once in awhile it will sound like it's in too high a gear and too low rpm),but I'm getting codes 172 (O2 sensor, which has been changed - TWICE), 327 egr position sensor (also NEW), and 332 insufficient egr flow (NEW egr & NEW egr tube).
I have also changed the egr vacuum solenoid as well as gotten rid of ALL the old junk plastic vacuum lines.

What am I missing?

 

"Almost didn’t get home with my 1994 F-150.
It is a 5.0 with E4OD,4x4 and has about 179,000 miles.. Could not get over 20mph and the transmission was slipping a lot.

Bought a OBD1 reader and the KOEO codes were 172,334, and 452.

172 HEGO (HO2S) sensor fault/lean
334 EGR closed valve voltage high
452 Vehicle Speed Sensor (VSS) signal fault."

I replaced the VSS (aka ABS) on the rear end. Check engine light went off. I decided to replace the REAR fuel pump. It went bad a couple of years ago. I also had the transmission serviced. When I bought the truck about 6 years ago the FRONT fuel pump was bad. I replaced it at that time. I routinely switched tanks until the rear pump went out a couple of years ago. While driving today I noticed symptoms similar to the original problem. On a long uphill pull the power dropped off again and when I accelerated the engine backfired. I switched the tanks and the truck took off like it dropped into passing gear! Thinking I was out of gas on the front tank I filled both tanks. Based on the amount of gas the front tank was not empty. Running on the front tank it happened again. Switching to the rear tank cleared it up again. The truck has been running on the front tank for a couple of years.
It occurred to me that maybe the problem was the front fuel pump or associated lines all along. I can’t determine if there are any filters related to each tank. I really don’t want to put another pump on right now. Anyone have any ideas?

 

The fuel filter is inside the driver side frame rail. If memory serves it's just behind the front edge of the bed. There's just the one filter that serves both front and rear tanks.

There is also a plastic mesh filter inside the tank, on the end of the fuel pickup tube. You will need to get to the top of the tank to examine it, either by dropping the tank or by removing the bed. If you drop the tank you are committed until you reinstall the tank; there are no valves in these lines as the check valve(s) in the in-tank fuel pumps are the only things keeping fuel from passing from one tank to the other in service.