EGR Cooler Failure — One of the Most Common 6.7 Failures
What Happens
The 6.7 Cummins EGR (Exhaust Gas Recirculation) cooler routes hot exhaust gas through a coolant-cooled tube bundle to lower its temperature before reintroduction. The internal tubes crack from thermal cycling — typically between 100,000–150,000 miles — allowing exhaust gas and coolant to mix.
Symptoms include white smoke from the exhaust, coolant loss with no external leak, and coolant smell from the intake. Left unaddressed, coolant entering the combustion chamber can hydraulic-lock the engine.
Our Repair Approach
- Pressure test the cooling system to confirm EGR cooler failure vs. head gasket
- Remove and replace the OEM EGR cooler with an upgraded aftermarket unit designed to resist cracking
- Flush the cooling system fully — old coolant contaminated with exhaust gas needs to be removed completely
- Inspect the EGR valve itself, which often needs replacement at the same time
CP4 Injection Pump Failure
The Problem with the CP4 in US Diesel
The Bosch CP4 high-pressure injection pump was designed for European ultra-low-sulfur diesel, which has better lubricity than US ULSD. In American trucks, the CP4 wears faster — and when it fails catastrophically, it sends metal shavings throughout the entire high-pressure fuel system: injectors, lines, rails, and the lift pump.
A full CP4 failure on a 6.7 Cummins can result in $8,000–$15,000 in damage if the contamination spreads before diagnosis.
Prevention and Repair
- We offer CP4 contamination testing to catch early-stage wear before catastrophic failure
- A CP4 replacement kit with diesel fuel additive (lubricity improver) can extend pump life significantly
- If contamination has already occurred, we perform full system flush of fuel rails, lines, injectors, and pump — no shortcuts
DPF, DEF, and Emissions System Issues
Common 6.7 Emissions Faults
- DPF (Diesel Particulate Filter) clogging — forced regeneration or replacement when passive/active regen doesn't clear it
- SCR (Selective Catalytic Reduction) failure — often DEF quality related
- DEF (Diesel Exhaust Fluid) sensor faults — incorrect concentration or contaminated DEF
- NOx sensor failure — upstream/downstream sensors triggering limp mode
We use professional diesel diagnostic scan tools that read manufacturer-specific Cummins codes — not just generic OBD-II. Proper diagnosis before replacing expensive components saves significant money.
Schedule Your Service in Chico, CA
Tedious Auto Repair — 2695 CA-32, Chico · Open 7 Days · (530) 826-4275