P3870
PowertrainEgr Advancedmoderate severityElectronic EGR Cooler Bypass Valve Stuck
What P3870 Means
The electronic EGR cooler bypass valve that routes exhaust gas around or through the EGR cooler is stuck.
Symptoms
- Check Engine Light
- EGR gas temperature incorrect
- Higher NOx emissions
- Reduced engine performance
- EGR cooler may overheat or underperform
- Intake manifold carbon buildup changes
Common Causes
- Carbon buildup on valve
- Actuator motor failure
- Valve mechanism corroded
- Wiring fault
- Exhaust condensation causing corrosion
Diagnostic Steps
- Command EGR cooler bypass valve via scan tool
- Monitor EGR gas temperature upstream and downstream of cooler
- Inspect valve actuator operation
- Test valve position sensor
- Check for carbon deposits on valve
Where to start: Replace EGR cooler bypass valve. Clean carbon deposits from EGR passages. Inspect EGR cooler for leaks.
🔌 Don't have a code reader?
Any of these will read and clear this code — pick by how deep you want to go.
Budget handheld~$40
ANCEL AD410 →
No-phone-needed handheld — reads, clears, live data, freeze frame.
✓ ANCEL official store
Serious DIY~$100
BlueDriver Pro →
Enhanced codes (ABS, airbag, TPMS) plus repair reports.
SHOP FAVORITEShop-grade tablet~$300
Autel MaxiCOM MK808S →
Bidirectional tests, service resets, all systems.
✓ Autel official store
Pro diagnostics$1,500+
Autel MaxiSys MS906 Pro →
Full-system pro platform — topology mapping, ECU coding, the works.
✓ Autel official store
As an Amazon Associate and Autel/ANCEL partner, OLP earns from qualifying purchases — how we link. This never changes the specs we publish.
Related Codes
Community Confirmed Fixes
No confirmed fixes yet for this code. Be the first to contribute!
Submit a FixFound a Fix for P3870?
Help other technicians by sharing what worked on your vehicle.
Submit Your Fix