Intermittently Lack of Power (Ghost)
Hello.
My customer brought this vehicle to me from the dealership because they can't seem to fix it there or can't seem to find the issue and he's tired of keep on going back and spending money on something he doesn't even need.
The main reason he took the vehicle to the dealership in the first place was whenever he's driving and come to a complete stop and try to pull off it seems like if the vehicle is holding back in either 2nd or 3rd gear and RPM do not move the way it supposes to unless he completely shuts off and restart and that's when everything goes back to normal.
DEALERSHIP REPLACED PARTS:
- Rebuilt Transmission (Around $4800)
- BCM ($560)
- Diagnostic (Around $480) - Total 3 times
- Now dealership want a customer to replace TCM, Underhood Fuseblock & Install wire from ignition fuse to TCM (Asking for $1600) - DECLINED
My customer wants me to replace Fusebox & TCM (Programming) - Which I did on his request but the main issue is there.
I do not want to get married to this vehicle so I want some advice where can I start with my diagnostic?
THANK YOU
I went for a test drive and finally felt a symptom which the customer was having but he completely explained it to me wrong so I'll describe it here the best way possible.
- Intermittently taking off from complete stop vehicle take off good but however, it stays stuck in 1st gear and will NOT shift into 2nd.
- The throttle percentage does move and the engine does rev up like it wants to accelerate but still won't shift into 2nd. The gear ratio stays at 3.98 when the problem is happening.
Hi Roy. I'm so sorry, I entered the VIN so I thought it will show up. 1GBFG154X… 2008 Chevrolet Express 1500 5.3L
Hello Dan. TCM is located in engine area right in front of HVAC unit on the right side of wall.
That sounds like the ecm that vehicle does not have a tcm it is combined with the ecm . Did you by chance monitor the 12 volt supply to the transmission ?
Hello Dan. I have actually very carefully monitor the 12v & Grounds going into TCM and when the problem is happening I do not see any drops or glitches.
What about the 12 volts coming out to the transmission at the transmission case connector ? If I’m not mistaken it is the red wire but to be sure look at wiring diagram . If it is truly starting in 2nd or 3rd gear it’s a good possibility you are losing your 12 volt feed .
I have also monitor that also and have steady over 12 volts. all athe time even if vehicle is acting up.
Does this vehicle have hyrdoboost brakes or vacuum assist booster?
Hello Jared. This has Hydroboost Brake Booster
Ok. Is it taking off in high gear, or lacking power in 2nd and 3rd after shifting out 1st? Does it have 4th?
Hello Jared. So basically Rebuilt Trans was installed at the dealership. So the way customer is describing the issue it seems like if vehicle is taking off in 2nd or 3rd gear. But when I monitor the date on scan PID it does show that its in 1st gear but vehicle doesnt seem like it it they way it accelerates because it feels very heavy on gear if something was holding back.
Okay, so when you feel the problem, the TCM is commanding 1st, but doesnt feel like it. I would personally monitor the Trans/gear ratio pid to verify what ratio it is launching in. If I'm not mistaken, that one should have it. One other curious question I have is is it intermittent, or occurs very regularly?
So the dealership replaced the transmission and the BCM because of the problem!!?
Yes. I can understand about the TCM but replacing BCM doesnt make any sense to me at all.
Yes doesn’t make sense at all! Sounds like a bunch of wasted money! Good luck with it.
Hi Doug. A lot of money wasted and main issue is still there. I'll explain everything properly to the customer and see what he really want to do now. :)
Take a look at the brake pressure sensor voltage value, especially the live value compared to the learned minimum value. If live value is higher than learned minimum, it's possible it was relearned KOEO, and running value is higher. Context: I had a similar issue on an Equinox, a random, but consistent power loss on takeoff. ABS module saw that higher brake pressure input and began mild…
I went for a test drive and finally felt a symptom which the customer was having but he completely explained it to me wrong so I'll describe it here the best way possible. - Intermittently taking off from complete stop vehicle take off good but however, it stays stuck in 1st gear and will NOT shift into 2nd. - The throttle percentage does move and the engine does rev up like it wants to…
When it does not shift to second did you look at the command from the computer is it commanding second ?
Is it possible that the brakes are locked up after coming to a stop? If that feeling of being held back stays until you shut the vehicle off, then jack up one wheel at a time or stop in your bay and use the hoist to see if they’re stuck before turning off the ignition. There are a couple TSB’s for brake booster problems.
That's what one of my original thoughts were. Thats why watching the ratio pid is so important. That can cut diagnosing that problem in half almost. I'd be curious if it will freely roll in Neutral when the concern is present
I went for a test drive and finally felt a symptom which the customer was having but he completely explained it to me wrong so I'll describe it here the best way possible. - Intermittently taking off from complete stop vehicle take off good but however, it stays stuck in 1st gear and will NOT shift into 2nd. - The throttle percentage does move and the engine does rev up like it wants to…
I went for a test drive and finally felt a symptom which the customer was having but he completely explained it to me wrong so I'll describe it here the best way possible. - Intermittently taking off from complete stop vehicle take off good but however, it stays stuck in 1st gear and will NOT shift into 2nd. - The throttle percentage does move and the engine does rev up like it wants to…
Hi Arsalan, I start with the 3 C's - Complaint, Cause, and Correction. C1 - On an intermittent fault I question the client on when this first started. Any work done, or anything happen shortly before this started? I’m not so concerned with what was actually done as that hasn't corrected the fault. (I am interested as I want to at least verify the 'repairs' were done professionally and not…
Hello Scott. I went for a test drive and finally felt a symptom which the customer was having but he completely explained it to me wrong so I'll describe it here the best way possible. - Intermittently taking off from complete stop vehicle take off good but however, it stays stuck in 1st gear and will NOT shift into 2nd. - The throttle percentage does move and the engine does rev up like it…
Trans range sensor think you have the shifter down into ”1” instead of “D”? Or brake switch stuck on?
Verified the brakes and its not stuck on or the switch, TRS is working fine also while looking on the DATA PID
Hi Arsalan, What scan tool are you using? Can you take a snapshot when the fault is occurring and post the data? I'd like to see the TCM data stream. Thank you,
Okay, on scantool, is it commanding 2nd? 3rd? The fact that it has first tells me that the solenoid electrical ckts should be fine. The fact that there are no DTCs is interesting...
Hello Jared. When the issue is happening by watching on scan PID "Command Gear" shows 1 (not 2 or 3)
My brain is all about inputs, inputs, inputs now on your problem. OSS Signal issue? I've seen the wires break in the insulation at the connectors. I take a pick and slightly tug on each wire at connector to see if it strecthes, indicating the copper is broke. I wouldn't think range sensor because your PRNDL would lead you to that quickly.
I'm going to install OEM VSS & Harness connector & going to run a new wiring VSS to TCM & I'll see if i can run new wire from OSS also and see how it works out.
I should have thought of oss signal but wouldn’t that cause the speedometer to stop working on that vehicle?
Hmm... just double checked theory and op. That might me the case... still leaning input ... thinking cap is still on
Looking at the wiring diagram and comparing it to theory and op... Speedometer gets vehicle speed reading from the ECM over GM Lan. The ECM gets VSS reading from ABS on pin 57 it looks. This has tricked me before.
Hello Robert. So I did test drove couple of miles and vehicle finally acted up again and I did notice that speedometer do not operate also. My bad luck is that I did not hook up a scan tool that time to monitor DATA PID on scan for speed.
I continue to drive the vehicle until it acted up and I had scan tool hooked up so I was able to verify that VSS on DATA PID was not reading. Replaced VSS (AcDelco) and so far everything is working fine & I drove almost 250 miles. Original VSS was delphi and I do not understand why it was not replaced at the dealership at the time when they installed Reman transmission.
Sweet! I'm a firm believer in having a scantool on basically any test drive. So many people jump to very expensive conclusions, dont they!? Onto the next one, right?!
Hello Jared. Scan tool is a very important part of the diagnostic. I'm still confused about if the original problem was VSS so how did dealership find out its a Transmission problem & BCM? LOL I love to fix other peoples mistakes, It helps me make more money :)