How I survived catalytic converter theft

Hack-Mechanic-CAT-converter-theft lead
Rob Siegel

I’ve written multiple times about my 2008 Chevy 3500HD Duramax diesel. How my former engineering job had largely abandoned the 28,000-mile truck when the company closed the building … how it became a gag-worthy mouse-infested mess … how I made a criminally low offer for it (that took four months to be accepted) … how I largely de-moused it … and how I thought I’d use it to buy and tow home a whole bunch of cars but instead have only moved two cars and a bunch of BMW parts with it, helped my niece move, made cardboard and motor oil recycling runs in it … and how I park it in a $50/month rented space about a mile from my house to make space in my driveway.

As if that isn’t enough, I never expected to add, “… and how I had to deal with a stolen catalytic converter.”

My discovery of the theft happened in a funny way. Prior to Thanksgiving, my wife had arranged to borrow one of those tall outdoor heaters from a friend so that we could put it on the back deck in case someone wanted to escape the crush of people inside for a bit—maybe have a beer and a private conversation outside. So, I walked over to the truck’s parking space (which is in the parking lot of a dance studio located right next to what used to be the town dump but is now the recycling depot), reconnected the batteries, and fired it up.

As soon as the truck was running, I could hear an unusual whirring sound, as if a blower fan was running. I never for a moment thought it could be a cut catalytic converter, as it wasn’t a big woof-y, truck-y exhaust sound. It was more the kind of air-movement sound a cooling fan makes if the viscous clutch is locked up. I opened the hood, but the sound wasn’t coming from there—it seemed to be emanating from below, near the center of the truck. I crawled under and guessed that the source of the whirring was the transmission. I realized this was the coldest it had been outside this season, and that I hadn’t changed or even recently checked the transmission fluid. Maybe that’s all it was.

So, I drove the truck on a quick errand to see if warming it up made the noise go away. It didn’t. When I got home, I looked for my mechanic’s stethoscope but couldn’t find it. I crawled under the truck again, listened to the noise, put my hands on the transmission pan, and convinced myself the noise was indeed coming from there. To avoid any damage, I decided not to drive it the 20-ish miles to pick up the heater and instead used the Winnebago Rialta (the little VW Eurovan-based RV). I made a mental note to, after Thanksgiving, take the truck into the local transmission shop, which had looked at the transmission on my Suburbans years back.

The Monday after Thanksgiving, I set the plan in motion. I started the truck, crawled under it a third time to verify the presence and location of the noise, then drove it two miles to the transmission shop. I described the “whirring” sound to the shop owner. “Whirring, not whining?” he asked. I nodded. He looked perplexed and came outside to look at it. He stuck his head under the truck, and immediately said the last five words I expected to hear:

“Your cat has been cut.”

Cat converter missing cut pipe
There’s supposed to be a catalytic converter in that 17-inch empty section. Rob Siegel

I was astonished—both that it had happened and that I had completely missed it. In my defense, aside from the exhaust sounding pretty much normal (particularly with the windows up), the cut sections of pipe where the catalytic converter once resided are close to the inside of the right frame rail. Even after the guy told me what had happened, I had to crawl way under and look up and to the right to see the cut pipes. On the drive back from the transmission shop, I did notice that I could hear more spin-down noise from the turbo on deceleration than I remembered. I assume that it’s the turbo’s presence in the exhaust (rather than having an open pipe coming down from the exhaust manifold) that made it not sound like a straight-piped menace.

Cat converter missing cut pipe end
The rear section where the cat was cut … Rob Siegel
Cat converter missing cut pipe end
…and the front. Rob Siegel

Catalytic converters are stolen because they contain the valuable rare metals platinum, rhodium, and palladium to catalyze (react with) the exhaust. The scrap value is widely quoted online as being between $300 and $1500. Toyota Priuses are prime targets for cat theft because the hybrid vehicle’s cat contains a higher concentration of these precious metals than most other cars. Catalytic converter theft has been a hot topic for awhile, but it has accelerated dramatically in recent years, reportedly because mining of these materials was affected by the COVID-19 pandemic. In early November, there were news reports of federal authorities busting a company in New Jersey and arresting a nationwide ring of cat thieves, and there is legislation advancing at the state level to engrave the Vehicle Identification Number (VIN) into cats as a theft-deterrent. Diesel trucks used to be overlooked due to their cats working differently—they don’t contain rhodium, and thus having much lower recycling value—but their high ground clearance and easy cat access has recently made them targets.

I, of course, never gave any of this a second thought. I live in Newton, Massachusetts, one of the safest small cities in the country. I haven’t had a vehicle vandalized since we moved here from Boston 30 years ago. And I don’t own a Prius.

When it happened, of course, hindsight kicked in. This is a big dually truck that you can practically limbo under while wielding a battery powered Sawzall. My parking spot in the lot next to the town recycling center is in an industrial area. And the fact that many people likely saw the truck sitting for weeks made it a likely target. It’s a wonder it didn’t happen sooner.

Random parking lot cars on sunny bluebird day
The truck in what I now realize was a vulnerable parking location. Rob Siegel

So, after you shake your fist and swear at the lowlifes who cut the cat out of your ride, what do you do? The basic sequence is:

  1. File a police report. My local police station is processing several cat thefts a day (“mostly Priuses”).
  2. Contact your insurance company to find out your coverage. If you file a claim, you’ll likely need the police report, which is why I listed it as the first step.
  3. Learn what the laws are in your state. That may be a rude awakening. California, for example, requires the catalytic converter in all vehicles to be either the OEM part or an aftermarket State Air Resources Board-approved unit, and prohibits generic catalytic converters that are based solely on physical shape, size, configuration, or pipe diameter. Other states are likely more accommodating, but you’ll need to check.
  4. Get several estimates. As with nearly any repair, having it performed at the dealership will be the most expensive option.

Be aware that, in addition to state laws, certain Federal laws are in play. The first is that, not surprisingly, it’s illegal to remove a cat and replace it with any kind of bypass pipe. Another is that it’s illegal to sell or install a used catalytic converter unless it has been properly recertified, which involves testing and labeling. I doubt that black helicopters are going to swoop down on you if you buy a used cat and install it yourself, but what it means is that established independent repair shops likely won’t want the risk of offering it to you as an option. And technically, it’s illegal to be operating the vehicle with the cat removed, although it would take particularly bad luck on your part for that to be discovered, and a police officer would need to be having a particularly bad day for you to be written up about it, especially if you had the copy of the police report of the theft with you.

Regarding the hazards of short-term driving of the vehicle with the cat cut out, there are several issues. The first is whether the remaining sections of the exhaust are dragging or scraping against anything, as along with the cat, the thieves may have chopped out a hanger that supports the center of the exhaust. If you hear scraping, unless you’re a mechanic and can either ascertain that it’s a trivial issue or wire the exhaust in place, don’t drive the car—call for a tow.

Then there’s the health issue of the presence of exhaust fumes that are now likely gushing out directly under the car. This is the kind of thing you don’t want to be wrong about, particularly if you’re about to drive in traffic with children or infants as passengers. Err on the side of safety. The third is whether it’s harmful to the engine to drive with the exhaust open and the cat missing. For short distances, like to get the car repaired, it’ll likely be fine, but without the cat to clean the exhaust, the oxygen sensor after it (if it’s still there after the car was butchered with a power saw) is going to give readings to the vehicle’s electronic control unit (ECU), which will likely cause the check engine light (CEL) and potentially other dashboard indicators to come on. Depending on the car, it’s possible the ECU may throw it into a reduced-power limp-home mode. So, it’s best to drive it as little as possible.

In my case, I’m blessed with being a do-it-yourselfer and not needing to have the truck repaired quickly. After looking at the problem for a few days, here’s how it’s panning out:

  • The part that was taken—the OE General Motors “oxidation catalytic converter” (#15283013) used on trucks with Duramax LMM engines from 2007 through 2010—lists for $1837 with a $400 core charge (which, of course, I don’t have, BECAUSE IT WAS STOLEN). Discounted online dealer price is as low as $1200, but with the core charge, shipping, and taxes, it comes to nearly $1750. Plus, there’s a gasket, a clamp, and a hanger. You can see how if, you took it to a dealer, you could get quoted three or four thousand dollars for the job.
  • I have never, ever, deleted a catalytic converter from a car, and I have zero interest in starting now (yeah, I know; someone else already deleted it, but I need to do something to be able to drive the truck, and that is not going to be a bypass pipe).
  • I have a $2000 deductible on my truck’s comprehensive insurance. This means that I won’t be filing a claim and instead will either fix it myself or try to find some small low-overhead shop (e.g., not a dealer) to do it.
  • The original cat on the truck is welded between two pieces of double-walled 4-inch pipe. On the front end, it’s attached to the engine with a heavy-duty band clamp, and on the back end, has a four-bolt flange that’s bolted to the Diesel Particulate Filter (DPF). So, if I want to replace the whole cat assembly myself, it looks like it comes off fairly easily (or as easily as any old exhaust bolts come off).
Cat converter exhaust joint clamp
The band clamp at the front of the cat pipe. Rob Siegel
Cat converter missing cut pipe end
The top two of the four bolts of the flange holding it to the DPF. Rob Siegel
  • When the cat was removed, so was the post that a rubber hanger attaches to, so the front part of the back of the exhaust is currently just resting on a frame cross-member. I’m lucky that it is, or the whole thing could’ve tilted down and ripped out the lines plumbing the DPF. Even the cat notwithstanding, I’d be foolish to drive it anything but short distances at low speed until it’s properly hung.
  • Instead of replacing the whole section, if I want instead to have someone weld a new compatible aftermarket catalytic converter into the existing pipes, it looks to me like there’s still enough of both pipes present to allow it. That is, if I can find someone to do it. I called two shops that have done custom exhaust work for me over the years. The first one won’t touch it, because they don’t know that much about diesels and aren’t sure which cat would be needed to properly play with the DPF. The second shop said they’d need to see it but ballparked it at $1500 job and said they couldn’t get to it for two weeks because—ready?—they need to install new cats in a fleet of 56 city trucks, all of which had them stolen.
  • A vendor on eBay sells recertified cats for GM trucks and has the one I need in stock, shipped, for about $800. That price initially went tilt with me, but now is looking pretty good.
Catalytic converter pipe
The $800 eBay recertified solution. Courtesy KGC Warehouse
  • Let’s say that, for the sake of argument, there wasn’t a law against installing an uncertified used cat, and that I went looking for such a thing as a less expensive option. What I may or may not have found after searching for several hours on Facebook Marketplace and Craigslist for a cat for a 2007–

10 Duramax LMM was one guy in northern Maine selling a complete low-mileage exhaust system for $650. When I hypothetically asked whether he’d sell me just the cat and ship it, he hypothetically declined.

  • I also may or may not have seen ads on Facebook Marketplace and Craigslist for inexpensive used cats from the previous generations of Duramax diesels (the ones before the DPF became a federally mandated component), and while the bends of the pipes and the connections on the ends look the same as mine, they’re not listed as cross-referencing. I posed a question on the Duramax Diesel forum, but no one answered it definitively. A friend who knows diesels (but not Duramaxes) says the cat on a diesel with a DPF is a diesel oxidation converter whose job is to oxidize the fuel being injected into the exhaust to create enough heat to burn the soot out of the DPF, and that the previous generation of cat wouldn’t do that. Thus, it’d be iffy to buy one of them. If I saw them. Or was even looking for them. Which I may or may not have been.
  1. Let me cut the weasel-wording. I’m a practical guy who tries relentlessly to contain cost on 13 vehicles, and this is a truck I barely drive. If the only two options were 1) Take it to the dealer and pay up to my $2000 deductible, or 2) Entertain the possibility of buying some cheap, used, high-mileage catalytic converter assembly that would hang and seal the exhaust but might not perform the intended emissions function due to age or compatibility or both, you can see how the second option might be tempting. And if my truck was high-mileage, finding another high-mileage cat like the one that had been taken might seem justified. However, this is a 28,000-mile vehicle. Even the legality notwithstanding, the idea of finding and installing a $150 200,000-mile cat just doesn’t sit well with me.

For all these reasons, I pulled the trigger on the $800 eBay recertified cat. After a bit of back-and-forth, the vendor (KGC Warehouse) was kind enough to knock $100 off the price, which was greatly appreciated, especially considering that it was the only correct click-and-buy recertified cat I could find.

Lastly, there’s the question of preventing it from happening again. In the Prius world, there are now click-and-buy cages and shields you can install that make the cat more difficult to remove. I haven’t seen such a product for the truck, but it’s probably not too difficult to fabricate an aluminum plate. But really, I’m hoping that simply parking the truck down at the end of the driveway of my house on my sleepy dead-end street instead of in the highly visible parking lot next to the town recycling center will make the difference.


If you’re like me, you absolutely hate to be put into a situation where you feel put over a barrel and have to pay an insane sum of money simply to regain functionality that you already had. After all, this isn’t something fun like fresh paint or a hot engine or new wheels or new Recaro seats—it’s a freaking catalytic converter that some scumbag stole. At least I’m getting out of it for closer to washing machine money than Hawaiian vacation money.


Rob Siegel’s latest book, The Best of the Hack MechanicTM: 35 years of hacks, kluges, and assorted automotive mayhem, is available on Amazon. His other seven books are available here, or you can order personally inscribed copies through his website,

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    Or, you could sell the Mastadon, and buy a Kei truck, which would do everything you describe, for a whole lot less money.

    1 – Rob: Sitting for weeks may increase the number of people who’ve seen it, but it only takes 2-3 minutes to steal. Coulda been gone the next day.
    2 – I am totally sympathetic to the commenters who threaten to hurt thieves, but is killing someone for even $2k worth what will happen to you? Plus around here (SF Bay Area) they or their lookout are often armed.
    3 – I know a Prius owner who is on cat #6, I am totally serious. I would long ago have built a box in the driveway to park over. But they carry floor jacks and bottle jacks so your design will have to be creative.
    4 – Aluminum is near worthless against saws/wheels. Nice soft gummy 304 stainless steel is really hard on saw blades and somewhat tougher against wheels. Costs more though. Looking into it for a friend’s new Highlander for sure.

    Rob, these thieves will likely target your truck again knowing they you WILL replace said CAT. Security Cameras do NOT deter these people either, as they wear hoodies and masks. Until law enforcement cracks down on scrap yards who pay cash, the theft of CATS will likely proliferate.

    The troll in me wants to leave a 75-76 VW Rabbit out as a bait car since a revised engine tune from VW made it at least 49 state legal to gut the catalytic converter and reinstall the empty shell. Imagine the multilingual swearing.

    Funny you shpuld highlight this scourge – I have been reading UK magazines and cat theft is a common problem there. I haven’t heard of it being prevsalent in Australia or N.Z. Roll on hydrogen!

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