Engine Controls - MIL ON/DTC P0191
TECHNICALBulletin No.: 09-06-04-022B
Date: January 28, 2010
Subject: Malfunction Indicator Lamp (MIL) Illuminated, Intermittent DTC P0191, Slow Fuel Rail Pressure (FRP) Decay, Wiring Harness Connections, Voltage Fluctuations/Interruptions (Follow Correction Information Below)
Models:
2006-2009 Chevrolet Express, Kodiak, Silverado
2006-2009 GMC Savana, Sierra, TopKick
Equipped With Duramax(TM) Diesel Engine (RPOs LLY, LBZ, LMM)
Please Refer to GMVIS
Supercede:
This bulletin is being revised to update the reprogramming emission controller warranty coverage period information. Please discard Corporate Bulletin Number 09-06-04-022A (Section 06 - Engine/Propulsion System).
Condition
Some customers may comment that the malfunction indicator lamp (MIL) is illuminated, or it illuminates intermittently.
The technician may find DTC P0191 set as current or in history.
Causes
- A slow fuel rail pressure (FRP) decay rate may exist, due to an accumulated but harmless varnish buildup on the fuel injectors.
- The wiring harness connections may exhibit incorrect crimping, corrosion or poor terminal tension.
- Aftermarket electrical equipment may be improperly installed on the vehicle resulting in an interruption or fluctuation in voltage to the engine control module (ECM).
- The ECM monitors the FRP sensor voltage signal at engine start up. If the voltage signal is greater than (high fuel rail pressure) a calibrated amount DTC P0191 can set.
- The ECM monitors the FRP sensor voltage signal at engine shut down , expecting a decrease to a low voltage signal (low fuel rail pressure) within a calibrated amount of time. If the voltage signal is greater than a specified value within that specific time period, DTC P0191 can set.
Correction
Verify the model year of the vehicle in order to determine which one or both of the following procedures to utilize.
For 2006-2008 Vehicles - Diagnose Possible Slow Fuel Rail Pressure Decay First
Important
DO NOT replace the ECM, the fuel rail pressure regulator, or the fuel rail pressure sensor for this condition.
1. Start and idle the engine.
2. Observe the Fuel Rail Pressure Sensor parameter with a scan tool. The parameter should be between 30-40 MPa, depending on engine coolant temperature (ECT).
3. Turn OFF the engine, and immediately turn the key to the ON position.
4. Using a stopwatch, observe the decay of the Fuel Rail Pressure Sensor parameter with a scan tool.
5. The Fuel Rail Pressure Sensor parameter should decay to less than 6.6 MPa within 15 seconds.
If the Fuel Rail Pressure Sensor parameter is more than the specified value within the specified time period, then reprogram the ECM.
Important
If a 2006-2007 LLY, LBZ vehicle has, as one of nine ECM module ID Part Numbers, Part Number 12632483, then reprogramming the ECM will not repair this condition. If a 2007i-2008 LMM vehicle had field action V1819 - 08142 ECM EEPROM - REPROGRAM ECM applied, then reprogramming the ECM will not repair this condition. All 2009 LMM's already have an extended rail pressure bleed down calibration.
A revised software calibration has been released to address this condition. Reprogram the ECM using the Service Programming System (SPS) with the latest calibration available on TIS2WEB. Refer to the SPS procedures in SI.
When using a multiple diagnostic interface (MDI) for reprogramming, ensure that it is updated with the latest software version.
When using a Tech 2(R) for reprogramming, ensure that it is updated with the latest software version.
During programming, the battery voltage must be maintained within the proper range of 12-15 Volts. Only use the approved Midtronics(R) PSC 550 Battery Maintainer (SPS Programming Support Tool EL-49642) or equivalent during programming.
For 2006-2009 Vehicles - Use The Following Testing Procedures
Important
DO NOT replace the ECM, the fuel rail pressure regulator, or the fuel rail pressure sensor for this condition.
Wiring Harness Conditions
A secondary cause of DTC P0191 may result from a poor connection at the pigtail connector, or the engine harness connector, incorrect crimps, corrosion, and/or poor terminal tension.
1. Inspect the six-inch pigtail connector, which connects the FRP sensor to the main engine harness for incorrect crimps, corrosion, and/or poor terminal tension. Refer to Inline Harness Connector End Views for the appropriate model and year, and Circuit Testing and Wiring repairs in SI.
2. Inspect the Engine Chassis Harness to Engine Harness connector for incorrect crimps, corrosion, and/or poor terminal tension. Refer to Inline Harness Connector End Views for the appropriate model and year, and Circuit Testing and Wiring Repairs in SI.
Voltage Fluctuations/Interruptions at Key Up
Voltage fluctuations at key up, which false trigger a DTC P0191 can be very brief (less than 1 second) and may occur due to any aftermarket equipment installed on the vehicle.
Important
Aftermarket electrical equipment should have a diode connected across the power circuit (coil side) of the relay or solenoid being used in order to prevent transient voltage spikes. For more information on this subject, refer to Corporate Bulletin Number 08-08-45-004A.
Inspect for the proper installation and operation of any aftermarket equipment that may interrupt/interfere with the ignition voltage to the ECM. Refer to Checking Aftermarket Accessories in SI.
The following list is an indication of some of the types of aftermarket equipment that upfitters install.
- Theft deterrent systems
- Relays or solenoids to operate the electrical system of a snow plow or salt spreader
- Handicap ramp safety interlock systems
- Internal and external communication and lighting systems
Warranty Information
For vehicles reprogrammed under the 5 year / 100,000 mile (160,000 km) DURAMAX(TM) Diesel Engine warranty, use the table above.
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