4L60E Transmission Troubleshooting Diagnosis
Diagnosing transmission issues can be tricky. This section tries to summarize the most common issues in such a way that you can click on the different buttons based on your current symptoms to finally come up with a potential solution.
Basic Diagnosis
Does the vehicle move at all when put in Reverse or any forward gear?
Yes – Move to the “Transmission Drives” section.
No – There could be an issue with the pump or fluid level.
Is the fluid level low?
Yes – add fluid.
No – Check if the pump is circulating fluid. You can use the test port (remove plug with 11mm socket/wrench) on the driver side above the range selector switch or unclip cooler line from transmission. This can get messy! Start the engine for a few seconds. If it is circulating, then fluid will gush out.
Is fluid circulating?
Yes – possible issue with Boost valve or pump.
No – Most likely a broken rotor inside the pump. Might need to replace the whole pump assembly if either surface of the pump was damaged by the broken rotor.
Transmission Drives
Put the transmission in Drive. Does it shift through all the gears?
Yes – check the miscellaneous issues section.
No – Check if you can shift it manually by selecting 1, as it builds speed, shift to 2, and finally to D.
Does the transmission NOT shift if D, but it does shift if you select the gears manually?
Yes – If it shifts manually, you most likely have a bad input sprag assembly. You need to disassemble the transmission and check the sprag.
No – Look through the miscellaneous issues section as you may have lost all forward gears.
Is the transmission slipping?
Yes – You need to take if for a test drive and determine which gears are slipping. Check the test drive section for more information.
No – Check the miscellaneous issues section.
Transmission Slipping
(You need to complete the test drive first)
Does it only slip when shifting from 2nd to 3rd gear, and is able to eventually shift to 4th gear? It should be around 35 MPH and it will slip for a few hundred RPMs before 3rd gear engages. This is called a flare shift.
Yes – You could just have a damaged Servo ring. Try replacing the stock servo with a Corvette servo, which increases the apply area and is able to hold better. This mainly applies for low mileage units.
If it is a high mileage transmission then it could also be the initial stage of an input drum leak (either around the shaft area or the checkball) that could eventually lead to full loss of 3rd and 4th gear.
No – It does not catch 3rd gear (or 4th gear) at all. See next question.
Is the transmission slipping when it shifts into 3rd gear, but never catches 3rd gear? It just acts like it is in Neutral unless you let the speed drop significantly.
Yes – The 3-4 clutch pack is burnt. You will need to diagnose what caused it during the rebuild. Replacing shift solenoids will not fix this as it is a mechanical issue.
No – Check miscellaneous issues section.
Missing gears (no slipping at all)
(You need to complete the test drive first)
Do you have to let off the gas for it to shift?
Yes – You are most likely missing 2nd and 4th gear. When this is the case, you can drive it up to 35 MPH and then let go off the gas and it will shift (to 3rd gear) and you can keep on building speed and get up to highway speeds without issues. If you pay close attention, it only shifts once. This is most likely a broken band or worn out Reverse Input Drum. The transmission will have to come out and be disassembled regardless of which one it is.
No – Go to the next question.
Do all forward gears work, but you are missing Reverse.
Yes – Most likely a damaged sun shell. The transmission will need to be disassembled.
No – Go to next question
Need to rev up the engine for Reverse to work?
Yes – possible issue with Boost valve, pump or stator sealing rings.
No – Go to next question.
Missing 2 forward gears? (without having to let go off the gas for it to shift) Possibly have a CEL code for a shift solenoid.
Only have 1st and 4th -> Sol A/Sol 1-2 stuck ON
Only have 3rd and 4th -> Sol A/Sol 1-2 stuck OFF
Only have 1st and 2nd -> Sol B/Sol 3-4 stuck ON
Only have 3rd and 4th -> Sol B/Sol 3-4 stuck OFF
Miscellaneous issues
Vehicle has difficulty or won’t move at all in Reverse and if you select Neutral, it will move forward.
The forward clutch pack might be welded together causing the forward clutch pack to be engaged at all times. That negates Reverse and will cause it to move forward in Neutral.
Transmission moves forward but will not shift at all. It feels sluggish off a complete stop, but can drive it up to highway speeds.
The transmission is most likely in “Limp mode”. Check that the plug is fully seated (if it is not, you might also get CEL codes) and check for electrical/wiring issues.
Transmission moves forward but will not shift at all AND speedomoter does not work. It feels sluggish off a complete stop, but can drive it up to highway speeds.
Check for CEL codes related to vehicle speed sensor (VSS) or replace the VSS. Only use ACDelco or buy an OEM sensor from the dealership.
No lock up in 4th gear
Check brake switch (it is an input for lock up to apply), TCC solenoid (can be replaced with just dropping the pan), TCC valve (can be replaced with just dropping the pan), converter regulator valve bore in valvebody.
Harsh 1-2 shift
Broken springs in the 1-2 accumulator; or stuck/cracked accumulator piston. If the transmission is 07 and up with tan or blue plug and this happens after a rebuild, you can try to reset the Transmission Adaptive Tables using a scanner that has that functionality.
1-2 Shift delay and harsh shifting
Check for faulty or jumpy TPS sensor – replace if readings are not smooth.
Engine stalls at stoplight.
Possible bad torque converter.
Transmission temperature rising.
Possible bad torque converter, clogged cooler/cooler lines, bad pump, dirty filter.
Transmission slips when taking a turn and then works fine.
Check fluid level, it might be low and the turn cause the fluid to shift so the pump cannot pull it in.
Slow or slipping Reverse
Wrong low reverse clutches or cracked Sunshell. You can try fluid additive or seal restorer.
Harsh shifts or slam engagement.
Failed EPC solenoid or erratic TPS signal.
Progressive soft shifts
Leaky boost valve, worn seals, low line pressure, or clogged EPC filter.
Torque converter shudder in 4th gear
Contaminated fluid or weak converter clutch; flush with BG products or use Lubegard Shudder Fix.
Fluid coming out the vent tube/hose.
Plugged cooler lines or overfilled pan — flush immediately.
Major Mechanical Failures
(Symptoms by component failure)
Fractured Sunshell
No reverse or 2nd gear (recommend upgrading sunshell to Sonnax or “Beast”)
Broken forward sprag
No movement in D/OD, only if shifting manually in 1, 2 and 3.
Damaged band or worn out reverse input drum
Need to let off the gas for the transmission to shift out of 1st gear. You will only have 1st and 3rd gear.
Snapped output shaft
Loud bang, loss of all gears
Worn planetary set
Whining in 1st and Reverse, quiet in 3rd.
Pump Failure
Fluid level doesn’t drop when engine runs. No movement in any forward gear or Reverse.
Front pump bushing walkout
Fluid leak at converter/bellhousing area.
Internal crossleak
Fused clutches or cracked housing
Needle bearings in oil pan
Planetary or torrington bearing failure
Common Fluid Failures and Leaks
Converter area leak
Front pump seal of bushing walked out – need to remove transmission and replace component.
Fluid coming out of vent tube
Cooler blockage or overfilled pan
Metal or Bearings in pan
Internal lubrication failure – rebuild needed
Runs fine when cold and stops running as it warms up
Dirty fluid, dirty filter, or damaged piston seals. Start with replacing filter and fluid.
Torque converter shudder
Contaminated fluid, weak TCC clutch (replace converter).
Contact
Us
4L60ETransmissionRebuild@gmail.com