EGR Low Flow DTC P0401 - keywords 6.6 cool cooler diesel engine exhaust gas idle LMM recirculation restrict restriction soot valve

This PI was superseded to update Recommendation/Instructions. Please discard PIP4380.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

A dealer may encounter a customer concern of a SES light and a DTC P0401.

Complete the current SI diagnostics for any trouble code or symptom found. If diagnostics were inconclusive it's possible the vehicle has a restricted EGR cooler.

Vehicles that have extended idle times are more susceptible to restricted EGR coolers. Please question the customer about idle times. Also question the customer about how often they notice the Diesel Particulate Filter "Clean Filter Message."

If the customer has noticed the clean filter message on a regular basis, please direct them to the Diesel Supplement Owners Manual for "Diesel Particulate Filter" and the "Diesel Particulate Filter (DPF) System Description" found in SI.

Understanding the DPF system operation is extremely important.

Note: Using the Owner's Manual Guidelines for driving the vehicle through a regeneration will help with the build up of soot.

If the vehicle has a P0401 and the customer does use the vehicle for extended idle times, the EGR cooler will have to be cleaned or replaced.

To verify if the EGR cooler is restricted monitor MAF sensor readings at idle.

Use the Tech2 to command the EGR fully open (which is 40 percent when using Tech2 special function).

MAF readings (at idle EGR commanded to 40%) on a clean properly operating EGR cooler will be around 10 to 15 g/s.

A dirty or partially clogged EGR cooler will have readings of 17 g/s or higher. Readings in this area may induce an intermittent DTC P0401.

At 21 g/s or higher the condition will no longer be intermittent, and the vehicle will probably set DTC P0401 on every drive cycle.

If the restricted EGR cooler has been verified, removing and cleaning the EGR cooler may repair the condition. When the EGR cooler is removed use either Simple Green or Krud Kutter following the process below. Order new EGR cooler gaskets to complete this repair.

1. Remove the EGR cooler following SI repair procedures.
2. Fill EGR cooler (exhaust openings) with Simple Green or Krud Kutter (cleaners are available at most hardware stores). Plugging one end of cooler and then filling the EGR cooler may also be helpful.
3. Soak for 15 minutes.
4. Flush with clean warm water.
5. Repeat until the cleaner and water run clear with out any soot (this may take a full gallon of cleaner to complete).
6. Dry EGR cooler, and test with low pressure compressed air, apply air at both ends. If no soot is blown from cooler in either direction the cooler is clean.

Evaluate MAF readings after cooler is cleaned. Replace the EGR cooler if the MAF readings are unacceptable

Note: Local radiator shops with ultrasonic cleaners will also clean EGR coolers effectively. Do not use any cleaners such as brake clean or other chemicals with any type of acid in the product. Brake cleaners will only harden the soot and make it more difficult to remove.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.