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hdgene
hdgene, ASE Certified Technician
Category: Transmissions
Satisfied Customers: 4784
Experience:  25 Years Automotive experience,ASE Master & L1 certified. Ford certified trans rebuilder
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Occasionally while driving, no particular conditions, The

Customer Question

Occasionally while driving, no particular conditions, The engine revs up, trans stops pulling . Then if throttle dropped to lower rpm, it comes back in and pulls fine. May not do it again for three weeks.
JA: How many miles are on the car? Is it an automatic or a manual transmission?
Customer: 130 K, 4L8E auto trans, Ithink.
JA: What is the model/year of your Chevy?
Customer: 2008 2500 express van
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: Trans shop put in a couple solenoids as a Hail mary. ( This guy also says you can put any old kind of red trans fluid in it and it will be fine???) He changed oil and uses bulk purchased "Mag 1"
JA: I'm 40 . Forty something.
Customer: I did not ask your age. But thanks for that. But....Are you married?
JA: No. I'm the Chevy Mechanic's Assistant.
Customer: Cool
JA: Anything else you think the mechanic should know?
Customer: The usual driver says it does not seems like a "slip". More like a switch or breaker or relay drops out and the trans just goes like into neutral.
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the Chevy Mechanic about your situation and then connect you two.
Customer: I am 66 and a bit of a motor head all my life.
Submitted: 6 months ago.
Category: Transmissions
Expert:  hdgene replied 6 months ago.

Hello, for one, you need to use the specified fluid that is marked on the dipstick to make sure you dont have any shifting issues. Did it have any diagnostic trouble codes stored prior to the solenoids being replaced? Any codes stored now? Will it come back into gear if you wiggle the shifter? Was any metal debris found in the pan when it was dropped to replace the solenoids?

Customer: replied 6 months ago.
No codes, before or after solenoids replaced. No ferrous and very little aluminum color, no flake. Wiggling shifter not tried by driver, just back off throttle and it came back and no more trouble for weeks. Wondering about likelihood of dropping transmission elec. power briefly, like from relay, fuse, or TCM dropping out briefly.
No disrespect, but website said a Chevrolet technician would address this issue. I think GM guy might just have seen this exact situation before and put me on the path.
Expert:  hdgene replied 5 months ago.

Not a problem, I was going to say if you wiggle the shifter and it pops back into gear it would be an issue with a electronic transmission range sensor, this would not set any diagnostic trouble codes sometimes. Otherwise, with the trans dumpin back into gear by backing off the throttle sounds like an internal hydraulic leak, either caused by a worn or knicked seal or valve body issue. Since it is an intermittent fault, this is the hardest part about isolating the concern. But with the mileage on the trans, it can be a worn or hard seal or valve sticking in the valve body.

Expert:  hdgene replied 5 months ago.

Hello, do you need more help with this concern?

Customer: replied 5 months ago.
The driver has not had another episode of the trans "drop out" since I put in for your help. But he mentioned to me yesterday, (a BTW), that when he is cruising the freeway on cruise control, that the cruise control will drop out altogether. Since his foot is not on the accelerator pedal, the engine does not rev up as it has when the transmission dropped out. However he is sure that they drop out of both functions is occurring simultaneously and are related.
So does that bit of information confirm suspicion about the module or control you mentioned before? Put me on the path to the root cause, please.
Expert:  hdgene replied 5 months ago.

If it is an issue with the transmission range sensor and dropped int neutral you would think the rpm would flare as it tries to throttle up and maintain speed. The cruise could be dropping out due to an issue with a brake pressure switch/stop lamp switch or problem with the servo that controls vehicle speed. I dont see them be directly related. But anything is possible. You would need to test the cruise system to see what might be causing this concern