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Stepper Motor Fault

JohnShead

JohnShead

Member
Messages
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Location
Kingsport, TN
I recently replaced my slipping transmission and after reassembly I inadvertently left the fuel heater unplugged. Whilst test driving I had 24° advanced timing with the associated knocking and of course a SES light with DTC 34 - Stepper Motor Fault. When I got home I attempted to retard the timing by rotating the IP but it made no difference. I started looking at the wiring behind the fuel manager to see what must be amiss as the motor was running perfectly prior to the transmission change. I discovered the empty socket for the fuel heater plug which I'm sure is a problem. Does anyone know if this alone could cause my symptoms and code or should I look for something else? I was about to pull the intake and check all the wiring below it but if this will fix it I'd rather not.
 
I agree with above.
Somebody can chime in but I don't think there is a connection between the fuel heater and the ECM.
In other words, I have not seen the fuel heater cause any DTC.
However, the short in fuel heater can cause fuse blow up but that happened when it is connected.

I would check with whatever was fixed before this happened.
I am not sure with trying to move the IP may have caused more problem, though.
Then you have to time the IP again to get it within the spec required for the engine to start and that has to be done at operating temperature not when engine is cold.
 
Yup, all of the above.
Need a scanning tool capable of at least reading the timing and timing off set.
Get engine to operating temp then go through the timing relearn procedure. See where the timing is then rotate the pump to make the adjustment, doing the timing offset relearn with each time the iP is rotated.
 
And NEVER move the pump with the engine running!!!
It gets annoying sometimes but will keep from destroying the pump. Seen it happen a couple times, once in a fleet shop and once in the dealership. There is a reason the manual says to always shut off the engine, and it isn’t danger of you hitting the fan.
 
Update: I was in error in the OP, it was the water in fuel sensor that was unplugged, IDK if the ECM adjusts timing in the case of water in fuel or not so maybe that was the reason for the advanced timing. I was replacing injectors & glow plugs (HT Leroy) when I posted originally so I had the intake bolts that clamp the injector lines removed to allow them to move enough to get at the injectors. I didn't want to pull the manifold to look for issues if it wasn't necessary so I posted to see if anyone knew of this issue before. After looking thoroughly at all the wiring in that mess at the back of the motor I found no pinched wires, and all grounds are clean and tight. The wires I could see around the IP looked okay too, so I just put it back together to test the plug theory without removing the manifold. I put the IP on my original marks and cranked up the old beast. She's running purrrfectly (sic) now.
Desired timing=Measured timing=8.4°

Sorry about the probably significant error in the OP but it's running great again.
 
Last edited:
Yesterday when the timing was right and I posted the update it was just a coincidence at that time. When it was way off and setting DTC 34 on my transmission test drive was coincidence as well. I took it out for an hour long drive with my Tech2 watching the desired and measured timing and it intermittently would go to 24° and clatter like heck for a bit then it would settle down to match desired timing for long periods. When it only lasted a short time it didn't set the code, longer periods would. When it was matching the measured timing would be fluctuating rapidly at times but not far off from desired. I ruled out the transmission R&R as being the cause and I really didn't think the unplugged water in fuel sensor would cause this error either, so I now knew that there was another intermittent electrical problem (I've been chasing those down for a while now in this 26 year old truck with all of its broken plug latches having to be zip tied together.) So I took all of the wiring harness plugs apart and cleaned the females with a small drill bit, blew them out, squeezed them together slightly with a pick tool, and added a bit of electrolytic grease into them. I cleaned the males with 1000 grit sandpaper and blew the dust out. When I took the plug out of the IP it had the grease in it from long ago when it was first installed but it was real brown looking burnt (I believe this was the culprit), not like the clean grease some of the others had. I guess the grease can't tolerate the heat in the IP. I cleaned them up, plugged it in with no grease to burn, and took it on another hour long test. The whole time measured equaled desired with absolutely no fluctuation. This problem has most likely been happening for a while but since it usually didn't set the code I didn't know it. Now it's finally solved!
 
Truk Lite makes an anti corrosion grease. It is very thin and spreads easily. It is designed to prevent corrosion in bulb sockets. I use an acid brush for spreading the stuff and apply a very light thin coat to electronic connectors and to most any other electrical connector tjat I have worked on.
I have never trusted dielectric compound grease, ot seems to thick and heavy. One thing about the dielectric compound, it is silicone and silicone has the capability to resist moisture intrusion. For some reason, dielectric grease has just seemed way to thick. I would rather use Lubriplate engine assembly lube as it has a thinner and easier to smear than dielectric compound.
Just My mental musings, nothing to het excited about. 😹😹😹
 
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