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What P0420 means for your Traverse
Your catalytic converter is no longer cleaning exhaust gases effectively. On 2009-2017 Traverses with the 3.6L V6, timing chain stretch causes cam timing errors that lead to rich misfires and damage the cat. GM extended warranty under Special Coverage 10299 addresses early-model chain wear. The ECM detects this by comparing upstream and downstream oxygen sensor readings. You will fail emissions but the car is generally drivable short-term.
Top Causes on the Chevy Traverse 3.6L V6
54%
#1 CAUSE
Timing Chain Stretch Causing Rich Misfire
The 3.6L LLT timing chains stretch prematurely (often by 80k-120k miles). Stretched chains skew cam timing, throw P0008/P0009/P0017 codes, and cause rich-running conditions that overheat the cat. Once timing is restored, the cat is usually already damaged and must be replaced. GM Special Coverage 10299 extended chain warranty on 2007-2010 models.
Parts
$800-$1,600
Labor
$1,200-$1,800
Total
$2,000-$3,400
30%
#2 CAUSE
Direct-Injection Carbon Buildup
The DI 3.6L coats intake valves with carbon because no port fuel washes them. Heavy carbon causes uneven cylinder filling, misfires, and a long-term efficiency drop that triggers P0420. Walnut blasting at $400-$600 restores combustion and protects the new cat.
Parts
$30-$80
Labor
$400-$600
Total
$430-$680
16%
#3 CAUSE
Downstream O2 Sensor Failure
Each bank has its own pre and post-cat O2 sensor on the 3.6L. Post-cat sensors slow down after 100k miles, mimicking front-sensor switching and triggering false P0420. A scan tool with live data confirms.
Parts
$60-$160
Labor
$60-$120
Total
$120-$280
Most Affected Traverse Model Years
| Year | Engine | Trim | Typical Mileage | Notes |
|---|---|---|---|---|
| 2009-2012 | 3.6L LLT | LS, LT, LTZ | 90k-140k | Timing chain stretch; Special Coverage 10299 |
| 2013-2016 | 3.6L LFY | LS, LT, LTZ | 80k-130k | Updated chains but DI carbon issues |
| 2017 | 3.6L LFY | LS, LT, Premier | 70k-120k | Last year of LFY before LGX |
| 2018+ | 3.6L LFY/LGX | LS, LT, RS, Premier | 60k-110k | Improved but DI carbon still affects cat |
Is It Safe to Drive Your Traverse with P0420?
Short answer: Yes short-term, but if you have a rattle on cold start (timing chain) or active misfire codes, get it fixed quickly. Running rich for thousands of miles destroys the cat.
How to Diagnose P0420 on a Chevy Traverse
- Listen for cold-start rattle. A 1-2 second rattle on cold start on the 3.6L is classic timing chain wear. Pull P0008, P0009, P0017, P0019 codes to confirm. Chain replacement is the durable fix.
- Check Special Coverage 10299. 2007-2010 LLT engines had extended chain warranty. Bring your VIN to a Chevy dealer or NHTSA.gov.
- Inspect intake valves for carbon. If mileage is over 80k on a DI engine, walnut blasting before replacing the cat protects the new converter and improves drivability.
Want a full step-by-step diagnosis specific to your Traverse's year and mileage? Run a $5.99 AI diagnosis report with a printable summary you can show any mechanic.
Chevy Traverse P0420 FAQ
How long do 3.6L Traverse cats last?
On a healthy engine, 150,000+ miles. With timing chain stretch or DI carbon, often only 80,000-120,000 miles. Address the root cause to protect the new cat.
How much to replace both Traverse catalytic converters?
$1,400 to $2,800 with quality aftermarket parts and labor. The 3.6L has two cats (one per bank) and both usually fail together.
Should I do walnut blasting with my cat replacement?
If mileage is over 80k on the DI 3.6L, yes. Carbon-fouled valves cause incomplete combustion that ages the new cat quickly. Add about $400-$600 to your bill.
Is the Traverse timing chain covered under warranty?
GM Special Coverage 10299 extended chain warranty on 2007-2010 LLT engines. Most have aged out, but check your VIN with a Chevy dealer.
See all P0420 causes and vehicles → · Related Traverse issue: Timing P0008 →