K
4L80E headache....
jimmyd55
+1y
So... I traded two P.O.S.'s for a slightly polished turd. I knew when I bought it that it had a problem with the tranny but I was hoping it was just dirty. It is not that simple. I've spent the past two month (on and off) trying to get the tranny out of "limp" mode with no success.
Here's what I have:
'95 Chevy 2WD Dually with a 7.4L and a 4L80E tranny.
Here are my symptoms:
Will only shift between 2nd & 3rd but has reverse.
Problems revealed with an engine analyzer:
Bad MAP sensor - swapped.
Bad spark control module - swapped.
Bad Quad driver module
Bad ABS wheel sensor - checked and found section that feels like it was pinched (heading to the junkyard for a replacement).
Other work/testing I've done:
Could not find a downshift module for a 4L80E only a 4L60E. Changed the filter and shift solenoids. Checked for fluid on the tranny harness connector and it is leaking so the internal harness will need to be swapped, in the mean time I cleaned the connector with brake clean, blew it out with air and put dielectric grease in the contacts. Swapped the input speed and output speed sensors. I've checked the TPS and pulled the IAC and cleaned it (the code for the ABS is the same as the code for the IAC). Tightened all electrical connections to the bat. Swappped the ignition switch harness with a junkyard unit. Checked all fuses. Pulled an ECM from a junkyard van to test and this did not change the symptoms. Pulled out the meter and test light and started testing pins at the ECM and the tranny plug, I have bat & ign power to both.
My questions:
Will a faulty ABS sensor cable cause the tranny to go into "limp" mode?
When testing the pins with the ignition on I have 14.5 VDC on the 1-2 Sol. and 245 mVDC on the 2-3 Sol. does the ECM need to see certain perameters before it will allow the 2-3 to work? This is a ground switched unit.
I know I'm not listing some of the symptoms I've found but I can't think of anymore right now. I'm certain this issue is electrical but I'm not familiar enough with the system to know what steps to take next. I've been using the Haynes manual and the ATSG Tranny manual and have checked everything they have recommended.
Something else... this has a OBDI system in it. The only code I have found manually is on the ABS side. I had a local parts house hook a scanner up and it did not flash any codes. I took it to a local shop and they hooked up a Snap-on computer and found the codes for the sensors and modules.
Any help I can get would be greatly appreciated.
Thanks!
Here's what I have:
'95 Chevy 2WD Dually with a 7.4L and a 4L80E tranny.
Here are my symptoms:
Will only shift between 2nd & 3rd but has reverse.
Problems revealed with an engine analyzer:
Bad MAP sensor - swapped.
Bad spark control module - swapped.
Bad Quad driver module
Bad ABS wheel sensor - checked and found section that feels like it was pinched (heading to the junkyard for a replacement).
Other work/testing I've done:
Could not find a downshift module for a 4L80E only a 4L60E. Changed the filter and shift solenoids. Checked for fluid on the tranny harness connector and it is leaking so the internal harness will need to be swapped, in the mean time I cleaned the connector with brake clean, blew it out with air and put dielectric grease in the contacts. Swapped the input speed and output speed sensors. I've checked the TPS and pulled the IAC and cleaned it (the code for the ABS is the same as the code for the IAC). Tightened all electrical connections to the bat. Swappped the ignition switch harness with a junkyard unit. Checked all fuses. Pulled an ECM from a junkyard van to test and this did not change the symptoms. Pulled out the meter and test light and started testing pins at the ECM and the tranny plug, I have bat & ign power to both.
My questions:
Will a faulty ABS sensor cable cause the tranny to go into "limp" mode?
When testing the pins with the ignition on I have 14.5 VDC on the 1-2 Sol. and 245 mVDC on the 2-3 Sol. does the ECM need to see certain perameters before it will allow the 2-3 to work? This is a ground switched unit.
I know I'm not listing some of the symptoms I've found but I can't think of anymore right now. I'm certain this issue is electrical but I'm not familiar enough with the system to know what steps to take next. I've been using the Haynes manual and the ATSG Tranny manual and have checked everything they have recommended.
Something else... this has a OBDI system in it. The only code I have found manually is on the ABS side. I had a local parts house hook a scanner up and it did not flash any codes. I took it to a local shop and they hooked up a Snap-on computer and found the codes for the sensors and modules.
Any help I can get would be greatly appreciated.
Thanks!
someotherguy
+1y
ABS code shouldn't affect transmission operation at all.
That quad driver error implies your PCM is bad; with a bad PCM I would expect unpredictable results so you might want to sort that out first.
Being last year for OBD-I doesn't affect your troubleshooting; it has a full range of transmission trouble codes.
I'm not a trans expert, not even close, but I'm pretty sure what you're describing is not limp mode. Limp mode generally means you'll start out in 2nd, often be at full line pressure (firm/harsh shifts) and in many cases all other gears are inhibited.
So you have no 1st, no 4th? If you put it in [D] (overdrive) it starts out in 2nd, shifts to 3rd, and that's it?
1st and 4th both depend on the 1-2 solenoid, 2nd and 3rd do not, so that kind of implies a 1-2 solenoid problem, but - that *should* set a code 82 and give you only 2nd OR 3rd, but not both.
1st - 1-2 ON, 2-3 ON
2nd - 1-2 OFF, 2-3 OFF
3rd - 1-2 OFF, 2-3 ON
4th - 1-2 ON, 2-3 ON
With your buddy's Snap-on hooked up, you should be able to see the gear that is selected according to the range switch, commanded gear, status of the 1-2 and 2-3 solenoids, etc. and even the voltage reading at the trans control module, which might reveal if wiring is playing a part in the trans getting proper voltage. What I'm unclear on is what they mean by control module; I'm tempted to say that's just the PCM, not an internal transmission component.
My hunch is the range switch or its wiring/connectors. I don't really understand operational theory on the solenoids, but a solenoid or solenoid circuit problem should set a code, and you don't have any trans codes.
Richard
That quad driver error implies your PCM is bad; with a bad PCM I would expect unpredictable results so you might want to sort that out first.
Being last year for OBD-I doesn't affect your troubleshooting; it has a full range of transmission trouble codes.
I'm not a trans expert, not even close, but I'm pretty sure what you're describing is not limp mode. Limp mode generally means you'll start out in 2nd, often be at full line pressure (firm/harsh shifts) and in many cases all other gears are inhibited.
So you have no 1st, no 4th? If you put it in [D] (overdrive) it starts out in 2nd, shifts to 3rd, and that's it?
1st and 4th both depend on the 1-2 solenoid, 2nd and 3rd do not, so that kind of implies a 1-2 solenoid problem, but - that *should* set a code 82 and give you only 2nd OR 3rd, but not both.
1st - 1-2 ON, 2-3 ON
2nd - 1-2 OFF, 2-3 OFF
3rd - 1-2 OFF, 2-3 ON
4th - 1-2 ON, 2-3 ON
With your buddy's Snap-on hooked up, you should be able to see the gear that is selected according to the range switch, commanded gear, status of the 1-2 and 2-3 solenoids, etc. and even the voltage reading at the trans control module, which might reveal if wiring is playing a part in the trans getting proper voltage. What I'm unclear on is what they mean by control module; I'm tempted to say that's just the PCM, not an internal transmission component.
My hunch is the range switch or its wiring/connectors. I don't really understand operational theory on the solenoids, but a solenoid or solenoid circuit problem should set a code, and you don't have any trans codes.
Richard