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Tahoe / Yukon Service Manual

DTC P0685-P0687, P0689, P0690, P1682, P16BC, P16BD, or P16BF

Engine Controls and Fuel - 3.0L LM2 Diesel | Diagnostic Information and Procedures | Document ID: 5500658 DTC P0685-P0687, P0689, P0690, P1682, P16BC, P16BD, or P16BF Diagnostic Instructions Perform the Diagnostic System Check prior to using this diagnostic procedure: Diagnostic System Check - Vehicle Review the description of Strategy Based Diagnosis: Strategy Based Diagnosis An overview of each diagnostic category can be found here: Diagnostic Procedure Instructions DTC Descriptor DTC P0685 Engine Controls Ignition Supply Voltage Control Circuit DTC P0686 Engine Controls Ignition Supply Voltage Control Circuit Low DTC P0687 Engine Controls Ignition Supply Voltage Control Circuit High DTC P0689 Engine Controls Ignition Supply Voltage Feedback Circuit Low DTC P0690 Engine Controls Ignition Supply Voltage Feedback Circuit High DTC P1682 Ignition and Start Switch Circuit 2 DTC P16BC Engine Controls Ignition Supply Voltage Feedback Circuit 3 DTC P16BD Engine Controls Ignition Supply Voltage Feedback Circuit 3 Low DTC P16BF Engine Controls Ignition Supply Voltage Feedback Circuit 3 High Diagnostic Fault Information

Circuit * Short to Ground Open/High Resistance Short to Voltage Signal Performanc e
B+ — Relay Coil P0689, P1682 P0685, P0689, P1682, P16A7, P16AF — —
B+ — Relay Switch P0689, P1682 P0685, P0689, P1682, P16A7, P16AF — —
Control — Component P0689, P1682 P0685, P0689, P1682, P16A7, P16AF P0690, P16B3, P16BF —
Circuit * Short to Ground Open/High Resistance Short to Voltage Signal Performanc
Control — Relay Coil P0686, P0690 P0685, P0689, P1682, P16A7, P16AF P0685, P0687, P0689, P1682 —
* For detailed component terminal information, refer to: Diagnostic Aids

Circuit/System Description

Circuit * Description
B+ — Relay Coil Supplied directly from the battery.
B+ — Relay Switch Supplied directly from the battery.
Control — Component The output circuit is switched to 12 V to activate the component.
Control — Relay Coil The output circuit is switched to ground to activate the component.
* For detailed component terminal information, refer to: Diagnostic Aids
Component Description
K20 Engine Control Module The control module contains a microprocessor used to process input data to control outputs. The control module controls a series of actuators to ensure optimal engine performance. The control module does this by reading values from a variety of sensors, interprets the data and adjusts the engine actuators accordingly.
KR75 Engine Controls Ignition Relay Relays are used to control a high power circuit with a low power signal.

There are 2 ignition voltage circuits supplied to the ECM. The 2 circuits are supplied by 2 relay(s): KR73 Ignition Main Relay & KR75 Engine Controls Ignition Relay The ECM monitors and compares the voltages supplied by the relay(s). Conditions for Running the DTC P0685, P0686, P0687 Ignition and Start Signal = Greater than 11 V Frequency the DTC runs = Continuously — After the running conditions are met P0689 Engine Controls Ignition Supply Voltage Command = On Ignition and Start Signal = Greater than 9 V Frequency the DTC runs = Continuously — After the running conditions are met P0690 DTC P0685, P0686, P0687 = Not set Engine Controls Ignition Supply Voltage Command = Off — For greater than 2 s Frequency the DTC runs = Continuously — After the running conditions are met P1682, P16BC Engine Controls Ignition Supply Voltage Command = On Ignition and Start Signal = Greater than 5.5 V Frequency the DTC runs = Continuously — After the running conditions are met P16BD Engine Controls Ignition Supply Voltage = Greater than 11 V Engine Controls Ignition Supply Voltage Command = On Ignition and Start Signal = Greater than 9 V Frequency the DTC runs = Continuously — After the running conditions are met P16BF Engine Controls Ignition Supply Voltage = Inactive Frequency the DTC runs = Continuously — After the running conditions are met Conditions for Setting the DTC P0685, P0686, P0687 Control Circuit = Commanded state does not match the actual state — Greater than 2 s P0689, P16BD Engine Controls Ignition Supply Voltage Feedback Signal = Less than 5 V — For greater than 6 s P0690, P16BF Engine Controls Ignition Supply Voltage Feedback Signal = Greater than 4 V — Greater than 50 s P1682, P16BC The following parameters are not within 3 V of each other: Control Module Voltage Signal Engine Controls Ignition Supply Voltage Feedback Signal Engine Controls Ignition Supply Voltage Feedback 3 Signal Actions Taken When the DTC Sets DTCs listed in the DTC Descriptor category = Type B DTC — Exceptions listed below DTC P1682, P16BC, P16BD = Type A DTC Conditions for Clearing the DTC DTCs listed in the DTC Descriptor category = Type B DTC — Exceptions listed below DTC P1682, P16BC, P16BD = Type A DTC Diagnostic Aids Use the schematics to identify the items/configurations listed below: Terminal Identification

Circuit Configurati 1 oCnonfigurati 2 oCnonfigurati 3 oCnonfigurati 4 oCnonfigurati 5
B+ — Relay Coil 85 85 86 30 1
B+ — Relay Switch 30 87 30 86 3
Control — Component 87 30 87 85 5
Control — Relay Coil 86 86 85 87 2

Reference Information Schematic Reference Engine Controls Schematics Power Distribution Schematics Connector End View Reference Master Electrical Component List Electrical Information Reference Circuit Testing Connector Repairs Testing for Intermittent Conditions and Poor Connections Wiring Repairs DTC Type Reference Powertrain Diagnostic Trouble Code (DTC) Type Definitions Scan Tool Reference Control Module References Circuit/System Verification

  1. Ignition » Cycle Off and On & Cycle On and Off Verify a click can be heard or felt at the component when the ignition was cycled: KR75 Engine Controls Ignition Relay ⇒ If a click cannot be heard or felt Refer to: Circuit/System Testing ⇓ If a click can be heard or felt
  2. Verify the following parameters are within 3 V of each other: Engine Controls Ignition Supply Voltage Feedback Signal Ignition and Start Signal or Engine Controls Ignition Supply Voltage Feedback Circuit 3 Ignition and Start Signal ⇒ If not within 3 V of each other Refer to: Circuit/System Testing ⇓ If within 3 V of each other
  3. Verify the scan tool parameter: Engine Controls Ignition Supply Voltage Feedback Signal = The value should not spike or drop out. Engine Controls Ignition Supply Voltage Feedback 3 Signal = The value should not spike or drop out. – Perform the action while monitoring the parameter: Wiggle the harness and connector: K20 Engine Control Module Wiggle the harness and connector: X50A Fuse Block - Underhood ⇒ If the value spikes or drops out Repair as necessary » Wiring / Terminal(s) / Electrical Connector(s) ⇓ If the value does not spike or drop out
  4. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data. Verify the DTC does not set. ⇒ If the DTC sets Refer to: Circuit/System Testing ⇓ If the DTC does not set
  5. All OK. Circuit/System Testing
  1. Ignition/Vehicle & All vehicle systems » Off
  2. Remove the component: KR75 Engine Controls Ignition Relay
  3. Ignition » On / Vehicle » In Service Mode
  4. Verify a test lamp turns On between the test points: B+ — Relay Coil & Ground B+ — Relay Switch & Ground ⇒ If the test lamp does not turn On Replace the component: X50A Fuse Block - Underhood ⇓ If the test lamp turns On
  5. Connect a test lamp between the test points: B+ — Relay Coil & Control — Relay Coil
  6. Perform the scan tool control function: Engine Controls Ignition Supply Voltage » On and Off Verify the test lamp turns On and Off. ⇒ If the test lamp is always Off 6.1. Ignition/Vehicle » Off & Remove » Test lamp 6.2. Disconnect the appropriate electrical connector: K20 Engine Control Module 6.3. Ignition » On / Vehicle » In Service Mode 6.4. Test for less than 1 V between the test points: Control — Relay Coil @ Relay Socket & Ground ⇒ If 1 V or greater » Repair the short to voltage on the circuit. ⇓ If less than 1 V 6.5. Ignition/Vehicle » Off 6.6. Test for less than 2 Ω between the test points: Control — Relay Coil @ Relay Socket & The other end of the circuit @ Control module harness ⇒ If 2 Ω or greater » Repair the open/high resistance in the circuit. ⇒ If less than 2 Ω » Replace the component: K20 Engine Control Module ⇒ If the test lamp is always On 6.1. Ignition/Vehicle » Off & Remove » Test lamp 6.2. Disconnect the appropriate electrical connector: K20 Engine Control Module 6.3. Test for infinite resistance between the test points: Control — Relay Coil @ Relay Socket & Ground ⇒ If less than infinite resistance » Repair the short to ground on the circuit. ⇒ If infinite resistance » Replace the component: K20 Engine Control Module ⇓ If the test lamp turns On and Off
  7. Verify the fuse that supplies voltage to the following circuit(s) is not open: 5290 / 5291 — For the circuit that set the DTC. ⇒ If the fuse is open 7.1. Ignition/Vehicle & All vehicle systems » Off 7.2. Disconnect the appropriate electrical connector: K20 Engine Control Module 7.3. Test for infinite resistance between the test points: Output terminal @ Fuse & Ground ⇒ If less than infinite resistance » Repair the short to ground on the circuit. ⇒ If infinite resistance » Replace the component: K20 Engine Control Module ⇓ If the fuse is not open
  8. Verify a test lamp does not turn On between the test points: Control — Component @ Relay Socket & Ground ⇓ If the test lamp turns On 8.1. Ignition/Vehicle & All vehicle systems » Off 8.2. Disconnect the appropriate electrical connector: K20 Engine Control Module 8.3. Ignition » On / Vehicle » In Service Mode 8.4. Test for less than 1 V between the circuits: 5290 / 5291 @ Control module harness & Ground ⇒ If 1 V or greater » Repair the short to voltage on the circuit. ⇒ If less than 1 V » Replace the component: K20 Engine Control Module ⇓ If the test lamp does not turn On
  9. Ignition/Vehicle » Off
  10. Connect a 30 A fused jumper wire between the test points: Control — Component & B+ — Relay Switch @ Relay Socket
  11. Ignition » On / Vehicle » In Service Mode
  12. Verify the scan tool parameter: Engine Controls Ignition Supply Voltage Feedback Signal = Within 1 V of the battery voltage Engine Controls Ignition Supply Voltage Feedback 3 Signal = Within 1 V of the battery voltage ⇒ If not within 1 V of the battery voltage 12.1. Ignition/Vehicle » Off & Remove » Jumper wire(s) 12.2. Disconnect the appropriate electrical connector: K20 Engine Control Module 12.3. Test circuit 5290 / 5291 for less than 2 Ω between the test points: Control — Component @ Relay Socket & The other end of the circuit @ Control module harness ⇒ If 2 Ω or greater » Repair the open/high resistance in the circuit. ⇒ If less than 2 Ω » Replace the component: K20 Engine Control Module ⇓ If within 1 V of the battery voltage
  13. Test or replace the component: KR75 Engine Controls Ignition Relay Component Testing
  1. Ignition/Vehicle » Off
  2. Remove the component: KR75 Engine Controls Ignition Relay
  3. Test for 70 to 110 Ω between the test points: B+ — Relay Coil & Control — Relay Coil ⇒ If not between 70 and 110 Ω Replace the component: KR75 Engine Controls Ignition Relay ⇓ If between 70 and 110 Ω
  4. Test for infinite resistance between the test points: B+ — Relay Switch & B+ — Relay Coil B+ — Relay Switch & Control — Relay Coil B+ — Relay Switch & Control — Component B+ — Relay Coil & Control — Component ⇒ If less than infinite resistance Replace the component: KR75 Engine Controls Ignition Relay ⇓ If infinite resistance
  5. Connect a 3 A fused jumper wire between the test points: B+ — Relay Coil & B+ Connect a jumper wire between the test points: Control — Relay Coil & Ground
  6. Test for less than 2 Ω between the test points: B+ — Relay Switch & Control — Component ⇒ If 2 Ω or greater Replace the component: KR75 Engine Controls Ignition Relay ⇓ If less than 2 Ω
  7. All OK. Repair Instructions Perform the Diagnostic Repair Verification after completing the repair: Diagnostic Repair Verification Battery Distribution Engine Compartment Fuse Block Replacement For control module replacement, programming, and setup refer to: Control Module References