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Just got off the phone with a local mechanic that does a lot of work on old Fords. He mentioned I should check the front wheel brake sensors also. Are those even part of the speed sensor circuit? (I didn't think so). Also, does the 95 E series have the PSOM and RABS test connectors like the F150 and Bronco?
So it does have 4WABS. Front sensors seem to be fine - resistance increases as the wheels turn and the connectors have voltage.
Finally got my hands on a legit service manual. Manual says to check the PCM first. What am I looking for on the PCM? Corrosion? Damaged pins? Anything else?
Is the PCM part of the speed sensor circuit? I thought the PCM just received an input from the PSOM?
Seems any further diagnoses will be difficult without a breakout box. I may just go ahead and send off the instrument cluster for an overhaul and hope that solves the problem.
So it does have 4WABS. Front sensors seem to be fine - resistance increases as the wheels turn and the connectors have voltage.
Finally got my hands on a legit service manual. Manual says to check the PCM first. What am I looking for on the PCM? Corrosion? Damaged pins? Anything else?
Is the PCM part of the speed sensor circuit? I thought the PCM just received an input from the PSOM?
Seems any further diagnoses will be difficult without a breakout box. I may just go ahead and send off the instrument cluster for an overhaul and hope that solves the problem.
How many miles do you do you have on this thing?
can you find the terminal breakdown for the plugs on the back of the PSOM? Namely the VSS circuit?
can you find the terminal breakdown for the plugs on the back of the PSOM? Namely the VSS circuit?
It only has 59K miles!
Found the appropriate wiring diagram in the manual so now I can just trace the wires by color to the plug terminals! Will test after work (also picking up a new multimeter on the way home.)
I am definitely not an electrician... What exactly am I testing for and how do I test? One end of the multimeter to a solid ground and the other end to the terminal, checking for resistance of less than 5 ohms right? Anything else?
There is no continuity when testing VSS circuit at the PSOM connector plug. And the VSS circuit within the PSOM itself has continuity.
Resistance in the VSS circuit at the PSOM connector and the ABS data link connector is about 1900 ohms. VSS input and output at PSOM both seem to be grounded.
All speed sensors (rear axle, front wheels and tranny) are getting 1.4V with key on engine off. Haynes manual says it should be getting 10V and if not it's a problem with the PCM. I'm not convinced of that. By the VSS/4WABS diagram below, it doesn't seem the PCM would be part of the "Open speed sensor circuit."
So what's next? Follow the wiring harness around the van looking for damage? Somehow test the 4WABS module and/or PCM? 4WABS Wiring Diagram 1995 E-150
There is no continuity when testing VSS circuit at the PSOM connector plug. And the VSS circuit within the PSOM itself has continuity.
Resistance in the VSS circuit at the PSOM connector and the ABS data link connector is about 1900 ohms. VSS input and output at PSOM both seem to be grounded.
All speed sensors (rear axle, front wheels and tranny) are getting 1.4V with key on engine off. Haynes manual says it should be getting 10V and if not it's a problem with the PCM. I'm not convinced of that. By the VSS/4WABS diagram below, it doesn't seem the PCM would be part of the "Open speed sensor circuit."
So what's next? Follow the wiring harness around the van looking for damage? Somehow test the 4WABS module and/or PCM? 4WABS Wiring Diagram 1995 E-150
According to that diagram it is. (upper right notation) Yours has the same symptoms mine had when my speedo cluster went south. Speedo quit working and transmission went nuts.
According to that diagram it is. (upper right notation) Yours has the same symptoms mine had when my speedo cluster went south. Speedo quit working and transmission went nuts.
Ah ok, that makes sense. I'm pretty convinced it's not my speedo cluster. The speedo works fine.
I'm going to jack it up and test the speed sensors again... Should there be continuity between the pins of the sensor?
Ah ok, that makes sense. I'm pretty convinced it's not my speedo cluster. The speedo works fine.
I'm going to jack it up and test the speed sensors again... Should there be continuity between the pins of the sensor?
Your PSOM could have failed and the speedo still working---the transmission not shifting properly would be a good indication the PSOM is at fault. Because the PSOM is part of the "speed sensor circuit" the code could be accurate even if it doesn't specifically identify which part has failed or ceased working properly.
My experience here is installing a brand new 20XX cluster from a diesel fueled van into my 2003 gasoline E250 because the coolant temp gauge wasn't working. The "wrong" cluster had full function of gauges and warning lights but the odo wasn't working and the transmission wouldn't shift normally.
Since your chassis is a 1995 it could be different but as already said the schematic showing here does have the PSOM in the cluster as part of the ABS system.
Your PSOM could have failed and the speedo still working---the transmission not shifting properly would be a good indication the PSOM is at fault. Because the PSOM is part of the "speed sensor circuit" the code could be accurate even if it doesn't specifically identify which part has failed or ceased working properly.
My experience here is installing a brand new 20XX cluster from a diesel fueled van into my 2003 gasoline E250 because the coolant temp gauge wasn't working. The "wrong" cluster had full function of gauges and warning lights but the odo wasn't working and the transmission wouldn't shift normally.
Since your chassis is a 1995 it could be different but as already said the schematic showing here does have the PSOM in the cluster as part of the ABS system.
Hmm you could be right here but I definitely want to check a few more components before shipping my speedo cluster off. Especially since the VSS circuit within the PSOM has continuity. There is some brown crud (electrolyte?) on the PSOM circuit board so maybe it could use an overhaul either way.
I tested the resistance in the rear ABS speed sensor at 1900 ohms. Specs in the manual say that sensor should be 1400 ohms. Could the extra resistance be causing a break in the circuit? Could that be why the OD off light doesn't start flashing until about 25mph?
Hmm you could be right here but I definitely want to check a few more components before shipping my speedo cluster off. Especially since the VSS circuit within the PSOM has continuity. There is some brown crud (electrolyte?) on the PSOM circuit board so maybe it could use an overhaul either way.
I tested the resistance in the rear ABS speed sensor at 1900 ohms. Specs in the manual say that sensor should be 1400 ohms. Could the extra resistance be causing a break in the circuit? Could that be why the OD off light doesn't start flashing until about 25mph?
The rear speed sensor is pretty bullet proof. It's on the top of the rear end. The aftermarket sensors for this are crap. I replaced the one in my 96 E150 with one and the speedo fluctuated +/- 3 mph. SO bad I robbed a Ford unit off a 99 SD F250 to replace that one with. My original got beat up while I was doing a gear swap. Probably still works even with a dent in it.
Hmm you could be right here but I definitely want to check a few more components before shipping my speedo cluster off. Especially since the VSS circuit within the PSOM has continuity. There is some brown crud (electrolyte?) on the PSOM circuit board so maybe it could use an overhaul either way.
I tested the resistance in the rear ABS speed sensor at 1900 ohms. Specs in the manual say that sensor should be 1400 ohms. Could the extra resistance be causing a break in the circuit? Could that be why the OD off light doesn't start flashing until about 25mph?
The PSOM is an electronic device so DC resistance probably doesn't tell you too much how the actual circuit is or is not functioning. As far as any crud you're seeing on the PCB that could be from an overheated component that's leaked or otherwise failed to some degree.
By all means do whatever tests you feel are appropriate before sending the cluster off for repair. A best case scenario would be finding the correct year and fuel type cluster from a scrap yard for cheap and swap it in---that's not a fool proof test but it would maybe give you a better idea what the real problem could be.
You can use a PSOM from any 1995 or newer F or E series.
A 1992 - 1994 will work but may have some needle jumping.
You should be able to tell if the stuff on the PSOM board is from a leaky cap or not.
Grab two or three PSOMs from a pick and pull yard as they would not cost much and you can use them to test the VSS circuit to the Speed Control and the PCM.
The only thing that points to a bad PSOM is the Speed Control not working but could be a bad Speed Control Module.
You have a 4R70W transmission so it shifts off the OSS (Output Shaft Sensor) on the transmission.
You can unplug the PSOM and the transmission will still shift just fine.
You may also have problems with the ABS but it would not effect the Speed Control or the PSOM unless it was pulling the VSS signal train down but I dough that if the Speedometer is working OK.
You can use a PSOM from any 1995 or newer F or E series.
A 1992 - 1994 will work but may have some needle jumping.
You should be able to tell if the stuff on the PSOM board is from a leaky cap or not.
Grab two or three PSOMs from a pick and pull yard as they would not cost much and you can use them to test the VSS circuit to the Speed Control and the PCM.
The only thing that points to a bad PSOM is the Speed Control not working but could be a bad Speed Control Module.
You have a 4R70W transmission so it shifts off the OSS (Output Shaft Sensor) on the transmission.
You can unplug the PSOM and the transmission will still shift just fine.
You may also have problems with the ABS but it would not effect the Speed Control or the PSOM unless it was pulling the VSS signal train down but I dough that if the Speedometer is working OK.
Speed control doesn't work... The next component I plan to have a look at is the speed control servo/amplifier.
So you're saying the PSOM has nothing to do with how the transmission shifts? The OSS isn't part of the speed sensor circuit? I'm a bit confused by your reply. Would driving with the PSOM unplugged be a way to test if it is indeed the PSOM?
I am having problems with the ABS light coming on... Could the fact that the replacement ABS/VSS in the rear axle has more resistance than the oem sensor be causing the intermittent ABS light?
From what you're saying it seems like there could be multiple issues... I assumed all the components I am having problems with (ABS, speed control, transmission) were all part of the same speed sensor circuit that is open and throwing the code...
So you're saying the PSOM has nothing to do with how the transmission shifts?
With the 4R70W transmission the PCM computer does use the VSS input and may flash the OD lamp on the stalk if it no long has the VSS input but can still shift OK with the Input from the OSS.
Originally Posted by Zacto
The OSS isn't part of the speed sensor circuit?
The OSS is a direct input to the PCM. It is not part of the PSOM, Speed Control or 4 Wheel ABS circuit.
Originally Posted by Zacto
I'm a bit confused by your reply. Would driving with the PSOM unplugged be a way to test if it is indeed the PSOM?
With the PSOM unplugged you would not have a speedometer or speed control but you would still have the 4 Wheel ABS system and the transmission should shift OK.
My PSOM quit and was out for a week but my 4R70W transmission still shifted OK. This is what I am going by and I do not know the program inside the PCM.
Originally Posted by Zacto
I am having problems with the ABS light coming on... Could the fact that the replacement ABS/VSS in the rear axle has more resistance than the oem sensor be causing the intermittent ABS light?
I do not know much about the 4 Wheel ABS system but the VSS is AC voltage generator so it resistance is not important as long as it generates 3.5 volts AC @ 30MPH. Replacement VSS sometimes putout a weaker signal train then the OEM.
This image is for a truck but yours operates about the same. Attachment 277289
Originally Posted by Zacto
From what you're saying it seems like there could be multiple issues... I assumed all the components I am having problems with (ABS, speed control, transmission) were all part of the same speed sensor circuit that is open and throwing the code...
The PCM is the only one that can throw a code. The OD lamp is hooked to the PCM and not the transmission.
You might try unplugging the speed control module and see what happens.
Maybe it is the PSOM... plus the whole instrument cluster.
Worked up the courage to take the speedo cluster apart and discovered damage on the PSOM circuit board. Looks like what I thought was leaked electrolyte was actually a blown component. You can see the burnt component in the first image below. Also, it looks like there is some heavy build up on the capacitor there too. On the other side of the board, there seems to be some damage that could be severing the trace but I'm not sure - check out the second photo.
I also noticed an issue with the warning light connector on the back of the cluster that may be causing my ABS light to come on. Looks like some copper melted, bridging two of the connection points. Traced the circuit and one of them looks like it goes to the ABS light. This may explain why the ABS light comes on so randomly. You can see what I'm talking about in the last image below.
So looks like I will be sending the cluster off for an overhaul. Any recommendations for shops specializing in instrument cluster repair?
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