Howard Fupp

Hello - I read all posts about the problems described here. My 1996 Suburban K1500 5.7L (w/4L60-E, I believe [I'm an idiot, so some of this may not be completely accurate] ) and heavy duty trailering pkge, trans cooler, etc. -- just recently began NOT shifting UP into 3rd or 4th gears [overdrive?]. Had driven from CT to Tucson (2500 miles pulling trailer). Got rid of trailer load & drove around out there on very crappy roads another 2000 mi; then, back here to CT on interstates @ ~67 mph. Best mileage/performance I ever had (has ~ 140K miles on it). Until 45 miles from home when suddenly engine started 'revving' as tranny wud NOT go up into 3 & 4. Fluid level was/is high (an inch above top mark on stick); but good red color. Manually shifted into 2 and drove home slowly on back roads. One mechanic said 'codes' show bad '3-4
solenoid'; but he is way to busy to do any in-depth work, unfortunately, as he is excellent man. Went to sleazy looking/acting AAMCO guy and he tells me entire tranny needs replacement/rebuilding. I now read above comments and realize there may possibly be some Electronic issue w/sensors (VSS; etc.) & NOT require the $2500 the AAMCO guy wants !!!
The 'check engine' light came on shortly AFTER the malfunction first occurred. I will get another OBC II reading from my first trusted mechanic today and write down and post here later. However, ANY help/advice/suggestions will be appreciated. THX. signed - Old Stupid Guy still w/bullet holes from SE Asia.

jgrygar

Typhoon hit the nail on the head...an ABS / speed sensor was causing the problem.

i have a 1999 K1500 4x4 with 204k miles on it. Suddenly, when on vacation with a trailer and far, far from home, here's what started to happen:
1) When driving at freeway speed, vehicle would slip out of gear at random times
2) Engine RPM increased due to being out of gear, and the tach showed that as well
3) Speedometer went to zero, and odometer stopped turning.
4) This would occur for a second or so, then the speedometer would go to normal and the vehicle would go back into gear, then the problem wound occur again some seconds later, then would occur again within seconds or minutes without a pattern.
5) When I slowed down and moved the shift lever to 1st or 2nd, it would go into gear. With the shift lever in 3rd or D it would not.
6) On one occasion when slowing to a stop, I got momentary wheel lockup at about 10 mph and the ABS light went on. The light reset on next restart and did not recur

i was faced with towing my vehicle and trailer a long way home if I could not fix the problem. I looked at all the posts I could find. The one that mentioned the ignition switch did not fit the symptoms, because only the items I mention above quit working. The sensor, or related wiring, or maybe the ABS electronics, were most likely the cause IMO.

i found two speed sensors on my transfer case, both identical, and both near the rear output shaft. I traced what little wiring I had access to to look for an open or a pinch, and found no problem. Not knowing what sensor goes where, I decided to replace both of them.

After replacing the sensors, I crossed my fingers and drove. It's been three long days of driving now, and the problem has not recurred, so I will say I'm pretty sure that one of the sensors was bad. Whew!

BTW, there's no speedometer gear leading to these sensors as some have said. I can't be totally certain, but these look like Hall-effect sensors.

Joe Street



BFFB

Your Vehicle Speed Sensor has failed. If it’s 4WD it’s located just above the cross member on the driver side of the transfer case. Otherwise it on the rear of the transmission i believe. Just YouTube the repair. $20 5 minutes and a Crescent Wrench. Super easy.