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The seabird is right.... most "U" prefixed faults are can network based faults than sometimes correlate back to an engine fault code & are usually labeled as implausibility or rationality faults. Did you happen to retrieve this fault from the dash using the key cycles or via your XRT? The turbocharger speed sensor is a variable reluctance speed sensor. It consists of a coil of wire and an iron core. The target on the turbocharger shaft is a ground flat in the center of the shaft. As the flat on the turbocharger shaft spins past the speed sensor, a signal is generated. The ECM interprets this signal and converts it to a turbocharger speed reading. The ECM will light the MIL lamp immediately after this diagnostic runs and fails. The MIL lamp will turn off once the diagnostic runs and passes in four consecutive drive cycles.
Engine running, turbo speed estimate is greater than a calibrated threshold
The ECM calculates an estimated turbo speed. The fault is activated when the difference of speed from the Turbo Speed Sensor and the turbo speed estimate is greater than a calibrated value. The fault is also activated if the turbo speed sensor reading goes above a calibrated limit.
1) Use the accelerator pedal to accelerate the engine speed to a high idle (100%) and hold the engine speed at high idle for at least 20 seconds....Does (U)/P2579 come active?
Yes >> Go To 2
No >> Double check turbocharger speed sensor wiring/connectors for chaffing, abrasions, pinch points, oxidation, bent, spread or mis-seated terminals... If OK, diagnostics complete...perform road test/repair verification.
2) Turn Ignition off. Disconnect the Turbocharger Speed Sensor harness connector.
NOTE: Check connectors - Clean/repair as necessary. Measure the resistance of the Turbo Speed Sensor by probing (K540) Turbo Speed Signal circuit and the (K541) Turbo Speed Sensor ground circuit at the turbocharger speed sensor. Is the resistance between 600 and 1600 ohms?
Yes >> Go To 3
No >> Replace the turbocharger speed sensor & perform test 1 again.
3) Measure the resistance between ground and the (K541) Turbo Speed Sensor ground circuit in the sensor harness
connector of the ecm. (terminal 43). Is the resistance greater than 100k ohms?
Yes >> Go To 4
No >> Repair the short to ground in the (K541) Turbo Speed Sensor ground circuit.
4) Reconnect the turbocharger speed sensor harness connector. Disconnect the ECM harness connector.
NOTE: Check connectors - Clean/repair as necessary. Measure the resistance between the (K540) (terminal 42 of ecm sensor harness connector) Turbo Speed Signal circuit and (K541) (terminal 43 of the ecm sensor harness connctor) Turbo Speed Sensor ground circuit at the ECM harness connector. NOTE: The resistance of the turbocharger speed sensor circuit must not be more than 10 ohms greater than the resistance of the turbocharger speed sensor. The turbocharger speed sensor resistance was read in step 2. Is the resistance within 10 ohms of sensor resistance?
Yes >> Go To 5
No >> There is high resistance or an open circuit in the engine
harness. Otherwise there is a low resistance (short) across
the sensor circuits. Repair/replace engine harness.
5) Measure the resistance between ground and the (K540) (terminal 42 of the ecm sensor harness connector) Turbo Speed Signal circuit at the ECM harness connector. Is the resistance greater than 100k ohms?
Yes >> Go To 6
No >> There is a short to ground in the (K540) Turbo Speed Signal
6) Measure the resistance between the (K540) (terminal 42 of the ecm sensor harness connector)
Turbo Speed Signal circuit all other circuits in the ECM harness connector except the turbocharger speed (K541) (terminal 43) Turbo Speed Sensor ground circuit. Is the resistance greater than 100k ohms?
Yes >> Go To 7
No >> There is a short between circuits of the ECM harness.
Repair or replace the engine harness.
7) Reconnect the ECM harness connector. Start the engine. Use the accelerator pedal again to accelerate the engine speed to a high idle (100%) and hold the engine speed at high idle for at least 20 seconds. Does DTC (U)/P2579 become active during engine operation?
Yes >> Replace the ECM.
No >> The problem may exist in the turbocharger speed sensor circuit or it may exist with other vehicle electronic
components. The problem may have been corrected when the harness connections were re-connected.
Be certain that the ECM and chassis grounds are in good condition. Hope this may help if the fault is reoccurring or is presently active. Cheers!
"08 2500 Mega, AFE intake, bushwacker fender flares, H&S exhaust, Black Maxx, egr/cooler delete, 20" moto metal wheels wrapped in 35" Nitto Dune Grapplers & hid's.
Last edited by contentlynumb; 03-24-2010 at 06:43 AM.
The Following User Says Thank You to contentlynumb For This Useful Post:
Ken is correct, the U code can often be crossed to a P. I have just finished going through the code for the XRT files for HOT DAMN, NO Turbo Tuning. There was a software error in that code for the 2579 dtc. That error has been corrected and a new file has been uploaded to the H&S website for download. So if you guys were running the HOT DAMN NO TURBO TUNING, go update and it will take care of your issue.
If you are running a tune other than the one above AND getting a 2579 code, please let me know! I need to know which tune you are running and the year and transmission of your truck so i can get it fixed! Thanks!
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