4l60e problems - The 1947 - Present Chevrolet & GMC Truck Message Board Network

67chevy77 · 07-22-2011, 03:15 PM

I have a 99 gmc z71. I can drive the truck with no problems for 50 miles or more and the all of a sudden when I come to a stop it shifts real hard like it has a shift kit. It only does it every now and then so it doesnt happen often. And after it starts messing up I can I turn the truck off and go start it back it shifts fine. Anyone know what it with might be? Im thinking its the valve body or a sensor making it do that.

clinebarger · 07-22-2011, 03:55 PM

Have it scanned for PCS (pressure control solenoid) codes.

67chevy77 · 07-22-2011, 04:43 PM

Ill have to check that. I hooked up a scanner to it a while back and it wasnt throwing any codes.
Posted via Mobile Device

clinebarger · 07-22-2011, 11:46 PM

Check the transmission fluid level, What scan tool was used? Not all "generic OBD II" scan tools read "manufacturer specific codes"

67chevy77 · 07-25-2011, 06:38 PM

Fluid level is fine. I used the "red brick" snap on scanner.

clinebarger · 07-25-2011, 08:49 PM

A snap-on MT2500 will do the job. There has to be a code or codes now, Cycling the key....Then normal operation is a dead give away.

67chevy77 · 07-25-2011, 09:52 PM

Ill put the scanner on it again but I know last time it didnt have any codes. Nothing in the history either if I remember right.

67chevy77 · 08-03-2011, 11:02 AM

Still no codes. I just put the scanner on it and and normal driving the pcs duty % was anywhere from 47 to 52. But I couldn't get it to mess up to see if any of that changed.
Posted via Mobile Device

clinebarger · 08-04-2011, 07:04 PM

This is going to be interesting. I use my Tech II so much I forget what exactly the MT2500 shows for data,

Heres a test using Actual Amps vs Reference Amps on the pressure control solenoid....

1. Test drive the vehicle. During the harsh shifting issue, monitor the "PC Sol. Actual Current" vs the "PC Sol Ref. Current". The values should match.

2. If the amperage is always low (less than 0.50 amps), recheck the sensor input to the PCM.

3. If the amperage is normal or high during the shifts, perform the line pressure test.

4. If the line pressure is high vs. the amperage, install an ammeter in the circuit to confirm the "PC Sol Ref. Current" is being put out by the PCM. Using an ammeter installed on the Red/Black wire at pin 6 on the Red PCM connector.

5. If the ammeter shows no or lower than expected current, replace the PCM.

6. If the ammeter matches the "PC Sol Ref. Current" check the Pressure Control Solenoid (PCS) and or valve in the transmission.

Or put a PCS solenoid in it & see what happens.

07-22-2011, 03:15 PM	#1
67chevy77 Registered User Join Date: Jan 2009 Location: Saluda, Virginia Posts: 131	4l60e problems I have a 99 gmc z71. I can drive the truck with no problems for 50 miles or more and the all of a sudden when I come to a stop it shifts real hard like it has a shift kit. It only does it every now and then so it doesnt happen often. And after it starts messing up I can I turn the truck off and go start it back it shifts fine. Anyone know what it with might be? Im thinking its the valve body or a sensor making it do that. __________________ Justin 1977 chevrolet rebuilt 350 9 inches of lift with 40s 4.56 gears. Work in progress. 1967 4x4 -sold- 1988 reg cab short bed 4x4 -sold- 1999 GMC extended cab short bed new body style Lifted on 33s.

07-22-2011, 03:55 PM	#2
clinebarger Senior Member Join Date: May 2009 Location: Fort Worth, TX Posts: 6,370	Re: 4l60e problems Have it scanned for PCS (pressure control solenoid) codes.

07-22-2011, 04:43 PM	#3
67chevy77 Registered User Join Date: Jan 2009 Location: Saluda, Virginia Posts: 131	Re: 4l60e problems Ill have to check that. I hooked up a scanner to it a while back and it wasnt throwing any codes. Posted via Mobile Device __________________ Justin 1977 chevrolet rebuilt 350 9 inches of lift with 40s 4.56 gears. Work in progress. 1967 4x4 -sold- 1988 reg cab short bed 4x4 -sold- 1999 GMC extended cab short bed new body style Lifted on 33s.

07-22-2011, 11:46 PM	#4
clinebarger Senior Member Join Date: May 2009 Location: Fort Worth, TX Posts: 6,370	Re: 4l60e problems Check the transmission fluid level, What scan tool was used? Not all "generic OBD II" scan tools read "manufacturer specific codes"

07-25-2011, 06:38 PM	#5
67chevy77 Registered User Join Date: Jan 2009 Location: Saluda, Virginia Posts: 131	Re: 4l60e problems Fluid level is fine. I used the "red brick" snap on scanner. __________________ Justin 1977 chevrolet rebuilt 350 9 inches of lift with 40s 4.56 gears. Work in progress. 1967 4x4 -sold- 1988 reg cab short bed 4x4 -sold- 1999 GMC extended cab short bed new body style Lifted on 33s.

07-25-2011, 08:49 PM	#6
clinebarger Senior Member Join Date: May 2009 Location: Fort Worth, TX Posts: 6,370	Re: 4l60e problems A snap-on MT2500 will do the job. There has to be a code or codes now, Cycling the key....Then normal operation is a dead give away.

07-25-2011, 09:52 PM	#7
67chevy77 Registered User Join Date: Jan 2009 Location: Saluda, Virginia Posts: 131	Re: 4l60e problems Ill put the scanner on it again but I know last time it didnt have any codes. Nothing in the history either if I remember right. __________________ Justin 1977 chevrolet rebuilt 350 9 inches of lift with 40s 4.56 gears. Work in progress. 1967 4x4 -sold- 1988 reg cab short bed 4x4 -sold- 1999 GMC extended cab short bed new body style Lifted on 33s.

08-03-2011, 11:02 AM	#8
67chevy77 Registered User Join Date: Jan 2009 Location: Saluda, Virginia Posts: 131	Re: 4l60e problems Still no codes. I just put the scanner on it and and normal driving the pcs duty % was anywhere from 47 to 52. But I couldn't get it to mess up to see if any of that changed. Posted via Mobile Device __________________ Justin 1977 chevrolet rebuilt 350 9 inches of lift with 40s 4.56 gears. Work in progress. 1967 4x4 -sold- 1988 reg cab short bed 4x4 -sold- 1999 GMC extended cab short bed new body style Lifted on 33s.

08-04-2011, 07:04 PM	#9
clinebarger Senior Member Join Date: May 2009 Location: Fort Worth, TX Posts: 6,370	Re: 4l60e problems This is going to be interesting. I use my Tech II so much I forget what exactly the MT2500 shows for data, Heres a test using Actual Amps vs Reference Amps on the pressure control solenoid.... 1. Test drive the vehicle. During the harsh shifting issue, monitor the "PC Sol. Actual Current" vs the "PC Sol Ref. Current". The values should match. 2. If the amperage is always low (less than 0.50 amps), recheck the sensor input to the PCM. 3. If the amperage is normal or high during the shifts, perform the line pressure test. 4. If the line pressure is high vs. the amperage, install an ammeter in the circuit to confirm the "PC Sol Ref. Current" is being put out by the PCM. Using an ammeter installed on the Red/Black wire at pin 6 on the Red PCM connector. 5. If the ammeter shows no or lower than expected current, replace the PCM. 6. If the ammeter matches the "PC Sol Ref. Current" check the Pressure Control Solenoid (PCS) and or valve in the transmission. Or put a PCS solenoid in it & see what happens.



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