2007 Silverado 1500 LT 5.3 ext cab z71

Hey all, I've been dealing with this since 2016 rpm surge (200-300rpm) only happening in cruise control above 50mph. I've scoured the internet about possible torque converters, tcc valves, etc.. And most if not all of those have been hard surges as in jerking/chunking. This isn't happening in my case, just noticeable quick surge/pulsing (every second) and its not every time cruise is enabled but dang near 90% of the time. I've had it in a handful of shops and no one can replicate it. I've checked the atf and its well topped off. If anyone has any possible insight I would greatly appreciate it.

 

A failing TCC/TCC solenoid can present itself in the way you describe, but so can other components in the transmission.

The easiest way to determine if it’s the transmission or throttle/fuel is to monitor the signals of the transmission input speed sensor and vehicle speed sensor with a scan tool or OBD2 app that has a graphing function.

With the truck at cruising speed and the TCC active, watch for the signals to deviate from each other when the surging occurs.

If the transmission is working properly, the signals will remain synchronized with each other; if the transmission is slipping, the signals will show deviation from each other.

 

Hey Gumby I appreciate the info, I'll get the truck into a shop and maybe drive them to lunch while the scanners hooked up. My luck it wouldn't reproduce on its own.

 

Sometimes the simple things are overlooked, but do you know when the last time the fluid and filter were serviced? The level may be OK but if it’s dark and smells burned, it may be worthwhile to change it. I’d expect a fluid related issue to be consistent, but with computer controls as part of the equation, it’s always difficult to say.

One thing you can do to help the techs reproduce the concern is to narrow down the circumstances as much as possible. These questions may help with that:

What is the daily drive/commute like ( how much city vs highway driving)? How many stop lights/stops do you typically make between your home and the highway? For example, you leave home, hit a couple of stop signs/lights, pull off for some coffee/etc, then hit one more stop before the highway.

How long (in miles or minutes) does the truck need to be driven?

Will it only happen once the engine is up to operating temperature?

Does the AC being on or off make a difference?

​​​​​Does ambient temperature seem to have any effect (cooler mornings vs warm/hot afternoons)?

Are there any other related concerns, such as delayed engagement when shifting from park to reverse or drive? A normally operating transmission should complete those shifts within 1-2 seconds, so any longer than that should be considered delayed engagement.

Does it seem to happen more often on level ground or when going uphill?

The more specific you can be, the better the techs can pinpoint the cause. If the truck has to be driven for 10+ miles before the surging starts, and the techs are only test driving it 2-3 miles, then obviously it’s not going to happen for them.

 

I was able to get a scan tool on it and drove the county for 45 minutes with a tech and luckily enough the symptoms happened. Unfortunately the fancy snap-on solus edge didn't catch or show any codes. They checked fluid and its good (full, red and no burnt smell) It's Mostly flat/rolling hills where I live so no drastic shifting. And it happens regardless of the temp outside, ac on-off, time on road warmed up. There isn't any delayed shifts or hard shifting, also forgot to mention There are no lights on the dash. And the only thing I can find online is others in Subaru forums having similar issues stating it's a ABS wheels speed sensor. But wouldn't that show a code or something? Another weird thing is sometimes while driving after pressing cruise control button, nothing happens. So I then press the brake slightly and re-attempt cruise control and it engages. Could it also be a failing brake light switch?

 

I’m not saying it’s impossible for a faulty wheel speed sensor to cause the issue, but I think it’s unlikely. If it is a faulty speed sensor, and no codes are setting, then each sensor would need to be watched with a scope to get real time analysis of the signal.

Additionally, there wasn’t much integration between the cruise and ABS/TCS/VSES/etc in 2007. Other than basic communication and the brake pedal switch, the systems operate independently of each other, making a faulty sensor all the more unlikely.

​As for the brake pedal switch, its interaction with the cruise is a direct on/off control - if the PCM sees the brake switch being activated, it will disable cruise until the driver presses the set/resume buttons again. The PCM doesn’t automatically activate the cruise once the pedal is released.

Next time you notice the cruise won’t set, put your foot under the brake pedal and pull back - if the cruise sets, the switch is definitely in need of replacement.

If the transmission is ruled out, the next thing I’d be looking at is the throttle body - if the bore is dirty enough, it can cause the throttle plate to drag/stick/bind.