Transmission Woes

Caleb Diagnostician Mishawaka, Indiana Posted   Latest  
Case Study
Driveability
Electrical
2009 Chevrolet HHR LT 2.4L (V LE9) 4-spd (4T45-E)
P0752 — Shift Solenoid "A" Stuck On

This car came in with customer complaint of"seems like it won't shift". I pull a P0752 1-2 shift solenoid stuck on. Many times a transmission code like this will put the trans in a "limp home" mode. This can sometimes cause people to chase there tail because they will try to diag the limp home as a problem and dont understand its a symptom of the root issue. I clear the code and go for a test drive. Sure enough it will not shift into 2nd gear. Then it slams into 3rd. Without getting to in depth with the solenoid apply strategy the 1-2 solenoid is applied in first gear and released in 2nd gear. I come back and find the transmission is 3 quarts low on fluid. I correct the fluid level and go for another drive. There is still no 2nd gear apply. The TCM commands 2nd gear but the ratio never changes. At this point there is only really 2 things that can be the issue. #1 The 1-2 shift solenoid is mechanically stuck on or #2 There is a problem mechanically with 2nd gear causing it too never engage. However if that was the case the transmission would just slip when 2nd gear is commanded. But it never slips. Its just always stuck in first. So I access the TCM which is literally staring you in the face when you open the hood . The 1-2 and 2-3 shift solenoids are normally closed ON/OFF solenoid with IGN power in and ground side switched by the TCM. Book time to R and R a solenoid is 6.5 hours so we don't want to be guessing. I connect to the ground side control for both solenoids and put a current clamp around each control circuit. KOEO off I command the known good solenoid and capture this waveform. It pulls 430 milliamps with a nice pintle bump. I can also hear it clicking when I put a stethoscope on the transmission case.

diag​.​net/file/f4fmlh81w…

Next I command the suspect 1-2 solenoid. The amp draw is slightly higher at 500 millamps. I don't hear a click in my stethoscope. And the waveform tells the story. There is no pintle hump at all!!

diag​.​net/file/f1nlp667o…

This is the nail in the coffin for the solenoid. The customer declined the repair because no money. I just thought it was cool to prove this without having to remove and visually inspect the solenoid. Also you may say"how do you know it was stuck in the open position and not off"? I know this because if stuck off there would have been no 1st gear. Anyway till next time.

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Thanks
Brian Instructor
Parma, Ohio
Brian Default
 

Thanks for sharing Caleb, amazing what are scopes show us if we use them and know what good looks like. Keep it up!

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Albert Owner/Technician
Towanda, Pennsylvania
Albert Default
   

Thank you this is proof that a scope can save you a whole lot of time and as vehicles become more and more integrated with electronics the more shops will have to have this kind of training.

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Sam Mobile Technician
Flint, Michigan
Sam Default
 

This is a great example of " How can you properly diagnose this without a scope?" Simple. You can't Resistance would have been good Everything would have checked out and a guess would have been to replace the shift solenoid. Everybody knows there is not a transmission shop anywhere that would have done just the shift solenoid. Even though that is all that is needed. I truly appreciate your…

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Caleb Diagnostician
Mishawaka, Indiana
Caleb Default
 

Thanks Sam!

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Dominick Technician
Bernardsville, New Jersey
Dominick Default
 

Nice!

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