# P2598 with pending P0299



## MRO1791 (Sep 2, 2016)

If had this twice, can't find an intake leak and I clear it and it seems to operate normally. I monitor MAP pressure and command pressure and the track. This happens when the car is beginning a Regen in stop and go traffic, both times. Freeze frame data shows the last occurrence was at idle with a throttle command at 20%. Not sure what I should be looking for as a cause? EGR? Any ideas?

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## diesel (Jun 8, 2013)

I haven't seen this one posted before. Have you checked your intake hose clamps?


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## revjpeterson (Oct 2, 2013)

The codes are related to an underboost condition and a mismatch between commanded and actual VGT position. Since the VGT is controlled by vacuum, it could be related to the vacuum pump or lines, or it could be a fault in one of the sensors that monitor the actual boost and VGT position. A previous incident including these two codes (plus a third code) was the result of a rodent-induced vacuum leak. (http://www.cruzetalk.com/forum/201-...discussion/104106-1st-check-engine-light.html) There is a vacuum pump on the front, driver-side corner of the engine and two thin lines that go to the turbo, along with (I think) a third vacuum line going to the brake booster. Inspecting those lines for leaks might be a good step to take. The MAP reading inside the intake should be independent of the vacuum produced by this pump, since the pump exists to replace the consistent presence of a natural vacuum source in the Diesel engine. 

I'm not sure what the relation to the re-gen initiation would be, though, unless something about that process is impacting the turbo in some way.


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## MRO1791 (Sep 2, 2016)

diesel said:


> I haven't seen this one posted before. Have you checked your intake hose clamps?


Yes, I checked all the connections, both sides of the intercooler and the rest. Next time I might try a induction leak test with compressed air, but given the freeze frame data I'm thinking it is related to the pre-regen cycle.


revjpeterson said:


> The codes are related to an underboost condition and a mismatch between commanded and actual VGT position. Since the VGT is controlled by vacuum, it could be related to the vacuum pump or lines, or it could be a fault in one of the sensors that monitor the actual boost and VGT position. A previous incident including these two codes (plus a third code) was the result of a rodent-induced vacuum leak. (http://www.cruzetalk.com/forum/201-...discussion/104106-1st-check-engine-light.html) There is a vacuum pump on the front, driver-side corner of the engine and two thin lines that go to the turbo, along with (I think) a third vacuum line going to the brake booster. Inspecting those lines for leaks might be a good step to take. The MAP reading inside the intake should be independent of the vacuum produced by this pump, since the pump exists to replace the consistent presence of a natural vacuum source in the Diesel engine.
> 
> I'm not sure what the relation to the re-gen initiation would be, unless the negative pressure inside of the intake during re-gen initiation would be, though, unless something about that process is impacting the turbo in some way.



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## MRO1791 (Sep 2, 2016)

revjpeterson said:


> The codes are related to an underboost condition and a mismatch between commanded and actual VGT position. Since the VGT is controlled by vacuum, it could be related to the vacuum pump or lines, or it could be a fault in one of the sensors that monitor the actual boost and VGT position. A previous incident including these two codes (plus a third code) was the result of a rodent-induced vacuum leak. (http://www.cruzetalk.com/forum/201-...discussion/104106-1st-check-engine-light.html) There is a vacuum pump on the front, driver-side corner of the engine and two thin lines that go to the turbo, along with (I think) a third vacuum line going to the brake booster. Inspecting those lines for leaks might be a good step to take. The MAP reading inside the intake should be independent of the vacuum produced by this pump, since the pump exists to replace the consistent presence of a natural vacuum source in the Diesel engine.
> 
> I'm not sure what the relation to the re-gen initiation would be, unless the negative pressure inside of the intake during re-gen initiation would be, though, unless something about that process is impacting the turbo in some way.


Ironically, my first CTD had these codes, and it was mice and that exact same tasty vacuum cap ( now all stainless steel vacuum cap!). All vacuum lines and actuators seem fine, no evidence of mice on this second CTD. The freeze frame from the second occurrence is interesting, I monitor EGTs using Ultragage, I noticed it was beginning a Regen as I hit stop and go traffic.. then MIL... After that there was a persistent lag between commanded MAP pressure and actual. After reading and clearing the codes it's back to normal. It is as if the MIL condition kept a permanent low boost condition. I also noticed with the MIL on and under load, EGTs were varying much more than usual, even up to 1200! Which was enough for me to take it down to 5th to lower EGTs. Seems like the lower MAP pressure to raise EGTs for a typical Regen was also causing higher EGTs here, no doubt higher soot load as well ( less O2 and more fuel = more soot). 

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