The left rear door on my 2011 Honda CR-V started making a chattering sound when locking and unlocking. After checking a CR-V owners forum, I ordered a door lock actuator from RockAuto. When the part arrived, I was excited to get the job done. I had already watched several videos about the repair. Everything the videos warned me about was true; the screws were extremely tight, space to wiggle the lock in and out is limited and the rod connecting the lock to the outside handle is tricky to get free because you can hardly see it. An hour and a half later, I had everything back together without breaking anything and no leftover parts. Time to check my work!

All went well until I got in the back seat and closed the door. It wouldn't open from inside! You have to transfer two original cables from the inside handle to the new lock actuator and I thought I might have messed something up there. I pulled it out a second time, opened it up and everything looked fine! What happened?! A little head scratching and it suddenly hit me - THE CHILD SAFETY SWITCH! Anyway, things get easier the more you do it. When I need to replace the next lock actuator, I believe it will be a 45 minute job.

James in South Carolina

Starting about twenty years ago, new diesel engines had to meet much stricter emissions regulations. Diesel Particulate Filters (DPF) and other emissions parts (urea injection, catalytic converters...) were added to the exhaust system between the engine and the muffler. Various sensors (temperature, nitrogen oxide (NOx), pressure...) enable the computers to monitor the performance of the system.

The DPF canister is responsible for collecting and burning off a diesel engine's telltale soot. At freeway speeds, the DPF may be able to passively heat up enough to burn off the soot. However, soot will start to build up in the DPF if the vehicle mostly just does short, low-speed trips around town.

The differential pressure sensor compares the pressures of the exhaust gas entering and exiting the DPF. A relatively large difference in pressure indicates the filter is becoming clogged with soot. A "regeneration" process will burn off the accumulated soot by actively heating up the DPF by burning additional diesel fuel in an upstream catalyst or some other means.

Typical Diesel Particulate Filter

Maintaining the differential pressure sensor and its plumbing is important. If the computer is not aware of a big pressure differential across the DPF then soot could seriously clog the DPF and start backing up into the engine. On the other hand, if the sensor incorrectly tells the computer there is a big pressure differential, then the computer could start doing too many stressful "regeneration" heat cycles.

The differential pressure sensor typically has one air hose/pipe plumbed into the exhaust before the DPF and one air hose/pipe downstream from the DPF. The sensor may be mounted in a relatively safe place in the engine compartment or it might be in a harsh (hot, dirty and wet) environment nearer the exhaust.

Typical Differential Pressure Sensor

Hopefully, the computer will recognize when the electronics in a sensor are failing and generating impossible voltages and subsequently turn on the check-engine light and record trouble codes (P2452-P2455). Unfortunately, it may take the computer longer to recognize a problem if soot, ash or other residue has partially blocked the upstream or downstream hose/pipe openings for the sensor. The pipes typically dead end at the sensor so gas does not flow through them. This helps prevent the hoses/pipes from filling with debris, but it also does nothing to keep debris from blocking the pipe entrances. Any soot and other crud building up on the wall of the exhaust pipe is free to eventually block the port(s) leading to the sensor.

Pressure could be increasing in the exhaust pipe upstream from the DPF but not be increasing in the partially blocked or torn open upstream sensor plumbing. The computer still sees a normal difference between upstream and downstream pressures and does not know soot is building up in the DPF. Hopefully, the computer will eventually realize something is wrong if blocked or leaking plumbing makes the upstream pressure impossibly less than the downstream pressure.

See the differential pressure sensor for your diesel-powered truck, SUV or car under "Exhaust & Emission" in the RockAuto.com catalog. Typically it is a good idea to periodically examine the sensor's hose/pipe for damage and run a pipe cleaner through it all the way to the exhaust pipe. Simply blowing compressed air through the sensor's hose/pipe and listening for the air entering the exhaust pipe might also be a relatively easy way to make sure the port in the exhaust pipe is not blocked (and air is not leaking to the outside). Of course make sure the engine is turned off, the exhaust plumbing is not dangerously hot, and you are following any applicable maintenance, diagnosis and repair instructions in the repair manual for your specific vehicle (found under "Literature").

Tom Taylor,
RockAuto.com

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