‘Never play parts darts’ Mechanics can’t figure out why mom of 4’s Suburban keeps going into limp mode, but I know what she needs to do
Okay, this one’s a toughie. @chelsearecommends is a self-described homesteader and mom of four. She drives a 2009 Chevrolet Suburban with what sounds like an intermittent electrical gremlin. It’s driving her crazy because after several trips to a few different mechanics, all she’s getting is head-scratching. Let’s try to help her out.
The Suburban is doing the same thing every time, but not all the time
Chelsea explains that the Suburban will randomly display system failures, after which the engine will go into limp mode. At that point, the engine loses power, and she has to pull over.
Once limp mode initiates, she has to park somewhere safe (which we can assume isn’t always all too safe) and turn off the engine. Then she waits a few minutes. After that, the Suburban will start and drive normally. That is, at least, until the next time limp mode triggers.
Chelsea says the dash messages and reduced power might happen three times in a single day, or they might not happen for a whole week.
She posted two videos explaining the misbehaviors. The thing that’s missing is any expert opinions or suggestions…even after she took it to different shops.
“It’s bizarre, and any time I bring it to the shop, it doesn’t happen.”
Of course, the comments sections on her videos lit up with guesses. But as one commenter advised, “Never play parts darts.”
What she needs is someone ready and willing to fix the Suburban…and they have to be familiar with 10th-gen GM diagnostics.
Here’s what she should actually do
I ran the service counter of a local shop here in the Midwest on and off since I turned 16, including a 10-year stint of full-time service advising. I’m nearing 40 now, by the way, so I’ve seen a thing or two.
Let me tell you: There’s nothing worse than a problem that only sometimes happens and goes away at the next engine cycle.
These intermittent problems are frustrating for everyone involved. Still, there’s a big, big difference between shops that shrug and give the car back and those that really want to fix it.
I was lucky enough to work for a team that always did the latter. I loathe shops that do the former…there are too many of them, but over time, they tend not to perform as well as the ones who care, for obvious reasons.
If I were a service advisor getting Chelsea’s call, here’s what I’d recommend we do:
Gather diagnostic and repair results to date, if any
All we’ve got at the moment, based on her videos, are the symptoms. If she’s got service records from these other visits, they might help a different shop get going.
Let a (highly reputable) shop keep the car until it goes into limp mode
If that’s a week, fine. She might have to be willing to part with several hundred bucks to fund the time spent driving and testing the car.
We used to have the technician drive a problem car to pick up their lunch, pick up a part, whatever.
But the truth is, there’s a lot a good mechanic can check upfront, even without an active failure. The hope would be that the shop that gets the privilege of diagnosing the Suburban is already familiar with what to do.
Which leads me to the next step…
Review the mechanical causes of a 2009 Chevrolet Suburban intermittently going into limp mode:
Check for stored or pending trouble codes. Even if the check engine light is off, a good scan tool can still pull useful data. Mechanics should look for stored or pending trouble codes and review freeze frame data.
This information shows what the sensors were doing when limp mode kicked in. That can point to failing parts or communication issues.
Inspect the throttle body and pedal position sensors. On GM trucks like the 2009 Suburban, throttle problems are a common cause of limp mode.
The throttle body can get carbon buildup. The throttle position sensor or accelerator pedal sensor can fail or send mismatched signals. The computer doesn’t like confusion. When it sees one, it limits power as a safety measure.
Check ground connections. Corroded or loose grounds are another frequent problem. GM trucks rely on good grounding to keep sensor data accurate.
Two grounds are especially important: G103 near the right cylinder head, and G104 on the frame under the driver’s side. A weak ground can cause sensors to misbehave and trigger limp mode.
Inspect the transmission control module and wiring. The TCM can fail or lose signal because of a bad connection or damaged wiring. That can interrupt communication and trigger limp mode.
Transmission fluid should also be checked. Burnt or dirty fluid might point to internal damage. The internal harness inside the transmission pan can also be a weak point.
Scan for communication faults between modules. GM uses a network called the CAN bus to connect control modules. If one module drops offline, the system might shut down power for safety.
A scan tool that reads communication codes (U-codes) can catch these issues. Common ones include lost signals from the engine or transmission computers.
Remove or inspect aftermarket electronics. Remote starters, alarms, or poorly installed stereos can interfere with vehicle electronics.
If the problem started after an accessory was installed, it may be the cause. A short or power spike can cause control modules to glitch and enter limp mode.
Road test with a scanner connected. If the problem only shows up while driving, a live scan is key.
A good mechanic should drive the Suburban with a scanner plugged in and data logging. Wiggling connectors while the engine runs can also help catch failing wires or loose plugs.
This isn’t a simple fix. It takes careful testing and experience with GM systems.
Stay committed to the process and pay attention to the repair timeline
Take plenty of notes and keep all records. Avoid double-paying for repairs. If a new shop fixes something done at another shop, she can request a refund from the previous places. That’s a whole other ballgame, though…right now, the focus is on getting the Suburban fixed.
The time spent dialing in on a gremlin isn’t always cheap or easy, but it’s better than continuing to pay people who can’t or won’t fix it over and over.
If she does go to a dealer, by the way, high reviews shouldn’t be from the sales department only. Look for five stars in the service area.
I’m curious to know what Chelsea ends up doing with the Suburban, and really hope she finds answers soon.
MotorBiscuit reached out to @chelsearecommends via TikTok direct message for comment.
