I came across a 2012 Duramax which was in reduced power mode due to poor Exhaust fluid quality (at least that was what was the text in the dash display).
This was reset with a GM tool appr 600 miles ago but now it happened again. First it lets you drive only 105 kph, then after a while only 88 kph and after a while it goes to limp home mode.
I downloaded the tune (which show the popup window "The data you just read isn't from your vehicle, your vehicle isn't readable...")). I read that this might be a signal that this tune was modified earlier?
I scanned all the DEF related data I could find from the scanner but I didn't get an idea of what detects the fluid quality. Can you help me with this what's going on in here? There are no dtc's present when I read with scanner.
If the Reductant Fluid Quality Test does not complete, or the Exhaust Fluid Quality Poor DIC message is difficult to clear, please follow the description and suggestions below.
If the vehicle has been in a cold climate condition, defined as -7C/20F or less over the last few days, it may be in “frozen tank status” which prevents the Reductant Fluid Quality Test (RFQT) from evaluating a result when triggered. Frozen tank status is entered when the vehicle key on event reads a DEF tank temperature below -7C/20F. The DEF tank temperature may be warmer after extended idles but only the conditions at key on are considered. To exit “frozen tank status”, the vehicle needs to be soaked in a warm garage for greater than 6 hours with the key off continuously. After this 6 hour key off event, make sure the DEF tank temperature is above -7C/20F immediately after key on. If not, it is necessary to repeat the soak procedure allowing the DEF tank to warm up above the -7C/20F threshold.
Note: When parking the vehicle outside to perform the RFQT it is important to monitor the ambient temperature. If the MAF senses intake ambient temperature below -7C/20F the test may not run correctly or timeout.
The Reductant Fluid Quality Test (RFQT) may not pass the first test or it may time out (45 minutes for LGH, 70 minutes LML). If the RFQT does not pass, run a DPF service regeneration followed by an ECM power down and then another RFQT. If after 2 attempts of this total procedure, the RFQT does not pass, it is probable a faulted condition still exists with the vehicle.
An ECM power down is required between repeated RFQT tests (Key off, remove the ignition key, and unplug the Tech 2 for up to two minutes between tests).
It is important to note whether an RFQT passes/fails versus a timeout event. Each of these could have a different root cause. For the case in which the test times out, one or more of the Conditions for running the DTC (as stated in the P20EE) were not met. There will not be any indication on the Tech 2 for which condition was not met. For the case in which the test fails, it is necessary to inspect the DEF system/components for symptoms of failure. The following guides can be used to help pinpoint the suspect component.
1. During the RFQT, the downstream NOx ppm should read roughly 70% less than the upstream NOx ppm on a healthy system. (As an example the upstream NOx ppm should be near 100ppm when the downstream NOx sensor 2 is around 30ppm or less).
2. During a DPF regeneration, the SCR is too hot to reduce NOx effectively. The upstream and downstream NOx ppm values should be relatively similar. NOx2 can be up to 30% higher than NOx1 in some cases.
3. During a road test at highway speeds (with system at operating temperature), the downstream NOx sensor should be 70% less than the upstream sensor and transition in the same direction as the upstream sensor, but at a much lower magnitude. During a road test, you can collect transient data for NOx1 and NOx2. After a heavy acceleration followed by a tip out (0 pedal), both sensors should go to zero while coasting down. If NOx2 does not go to zero shortly after NOx1, NOx2 is either faulty or the system is saturated with DEF. Performing this test during or shortly after a DPF regen prevents the system from being saturated with DEF.
4. If the above NOx sensor comparisons aren’t true, there are several possible causes. The NOx sensor cannot distinguish between NOx and liquid NH3 (DEF). High NOx sensor 2 readings can be caused by DEF getting past the SCR catalyst. This can be the result of a degraded SCR catalyst or a condition that causes excessive DEF in the SCR. After a DPF regeneration, the SCR system is purged of excessive DEF. It is easier to evaluate if an SCR brick is compromised right after a regeneration because it eliminates the extra DEF that the system was exposed to.
5. The SCR system can also store NOx in cold temperatures (extended idle). When the system warms up, this NOx can be released and results in a brief NOx2 increase above NOx1.
6. If NOx2 is malfunctioning or poisoned, NOx 2 values will be influenced and may be stuck higher than NOx1
7. This assumes that the DEF injector volume has been verified and passes with 3 distinct spray plumes from the injector.
8. This also assumes the intake and exhaust system are leak free. Intake and exhaust leaks can cause changes to the dosing system performance due to varied NOx output from the engine.
9. After-market components including, but not limited to, air induction parts, performance modifiers, grill covers, and exhaust modifications may negatively influence the DEF system performance. If all conditions above appear to be functioning normally, SCR replacement may be required but is a very rare occurrence. If the SCR is replaced, the new component will require a DPF service regen followed by the RFQT procedure
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