Scan Tool Unable To Communicate
NOTE:
KOER self-test failure or TOOL COMMUNICATION ERROR message could result if a failure is present in MAF sensor, TR sensor, VSS or related circuits.
Perform this test when instructed during QUICK TEST or if directed here by other test procedures. This test is used to diagnose the following:
- Standard Corporate Protocol (SCP) communication circuits BUS (+) and BUS (-).
- Wiring harness circuits (CHASSIS GROUND, PWR GND and VBAT).
- Faulty PCM.
- Verify Self-Test Procedure Is Correct
This DTC indicates KEY-ON-ENGINE-RUNNING (KOER) SELF-TEST cannot be completed. Ensure NGS tester is correctly attached to DLC, located under dash panel. Ensure NGS tester is not damaged or defective. If equipped with PTO, ensure PTO switch/actuator is in OFF position. Verify correct procedure was used to activate continuous memory, KOEO or KOER self-test. Correct as necessary. If no faults are found, go to next step. - Check VREF At Throttle Position (TP) Sensor
Turn ignition switch to OFF position. Disconnect TP sensor harness connector. Turn ignition switch to ON position. Measure voltage between SIG RTN terminal and VREF terminal at TP sensor harness connector. See Fig 2. If voltage is 4-6 volts, go to next step. If voltage is not 4-6 volts, see TEST C in appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE. - Ability To Access Continuous Memory Codes
If continuous memory codes are accessible, go to next step. If continuous memory codes are not accessible, go to step 7. - Ability To Activate KOEO Self-Test
If KOEO self-test can be activated, go to next step. If KOEO self-test cannot be activated, go to step 6. - Ability To Activate KOER Self-Test
If KOER self-test can be activated, DTC is false. Obtain PCM part number and check manufacturer for correct PCM application. If KOER self-test cannot be activated, go to next step. - Retrieve Any Continuous Memory Codes
Perform CONTINUOUS MEMORY SELF-TEST under QUICK TEST. If any continuous memory codes are present, service DTCs as necessary before continuing. If unable to retrieve any continuous memory codes, go to next step. - Check Voltage To DLC
Inspect DLC for damage and repair as necessary. Turn ignition switch to ON position. Measure voltage between terminal No. 16 (B+) at DLC and engine ground. See Fig 1. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, repair open in B+ circuit. - Check DLC Ground Circuit Continuity
Turn ignition switch to OFF position. Measure resistance between terminal No. 4 (CHASSIS GROUND) at DLC and chassis ground. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in CHASSIS GROUND circuit. - Check DLC PWR GND Circuit Continuity
Turn ignition switch to OFF position. Measure resistance between terminal No. 5 (PWR GND) at DLC and negative battery terminal. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in PWR GND circuit to DLC. - Perform Data Link Diagnostic Network Test
Turn ignition switch to ON position. Using NGS tester, perform DATA LINK DIAGNOSTICS test. If PCM: NO RESPONSE/NOT EQUIPPED, PCM: NO RESPONSE CKT 914 (BUS-) or PCM: NO RESPONSE CKT 915 (BUS+) message is displayed, go to next step. If none of the specified messages are displayed, no problem is indicated at this time. Repeat QUICK TEST . - Check Network Test Results
If NGS tester displayed CKT 914=ALL MODULE NO RESP/NOT EQUIP or CKT 915=ALL MODULE NO RESP/NOT EQUIP message after performing DATA LINK DIAGNOSTICS test, proceed as follows:- If only CKT 914=ALL MODULE NO RESP/NOT EQUIP message is displayed, go to step 12.
- If only CKT 915=ALL MODULE NO RESP/NOT EQUIP message is displayed, go to step 15.
- If both CKT 914=ALL MODULE NO RESP/NOT EQUIP and CKT 915=ALL MODULE NO RESP/NOT EQUIP messages are displayed, repair open to BUS+ and BUS- circuits or repair short between BUS+ and BUS- circuits and all associated modules.
If NGS tester did not display CKT 914=ALL MODULE NO RESP/NOT EQUIP or CKT 915=ALL MODULE NO RESP/NOT EQUIP message after performing DATA LINK DIAGNOSTICS test, proceed as follows:
- If CKT 914=SOME MODULE NO RESP/NOT EQUIP or PCM: NO RESPONSE ON CKT 914 (BUS+) message is displayed, go to step 14.
- If CKT 915=SOME MODULE NO RESP/NOT EQUIP or PCM: NO RESPONSE ON CKT 915 (BUS-) message is displayed, go to step 17.
- If both BUS (+) CKT 914 and BUS (-) CKT 915=ALL MODULE NO RESP/NOT EQUIP, go to step 20.
- Check BUS(+) Circuit For Short To Ground
Turn ignition switch to OFF position. Disconnect PCM 104-pin harness connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Measure resistance between chassis ground and PCM harness connector terminal No. 16 (BUS+). If resistance is more than 50 ohms, go to next step. If resistance is 50 ohms or less, a short to ground in BUS(+) circuit or associated modules exists. See appropriate MODULE COMMUNICATIONS NETWORK article in ACCESSORIES & EQUIPMENT. - Check BUS(+) Circuit For Short To Power
Turn ignition switch to ON position. Measure voltage between PCM harness connector terminal No. 16 (BUS+) and chassis ground. If voltage is one volt or less, go to next step. If voltage is more than one volt, a short to power in BUS(+) circuit or associated modules exists. See appropriate MODULE COMMUNICATIONS NETWORK article in ACCESSORIES & EQUIPMENT. - Check BUS(+) Circuit Continuity
Turn ignition switch to OFF position. Measure resistance of BUS(+) circuit between PCM harness connector terminal No. 16 and DLC terminal No. 2. See Fig 1. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in BUS(+) circuit to DLC. - Check For Short To Ground
Ensure PCM is disconnected. Measure resistance between PCM harness connector terminal No. 15 and chassis ground. If resistance is more than 50 ohms, go to next step. If resistance is 50 ohms or less, a short to ground in BUS(-) circuit or associated modules exists. See appropriate MODULE COMMUNICATIONS NETWORK article in ACCESSORIES & EQUIPMENT. - Check For Short To Power
Turn ignition switch to ON position. Measure voltage between PCM harness connector terminal No. 15 and chassis ground. If voltage is 6 volts or less, go to next step. If voltage is more than 6 volts, repair a short to power in BUS(-) circuit or associated modules exists. See appropriate MODULE COMMUNICATIONS NETWORK article in ACCESSORIES & EQUIPMENT. - Check BUS(-) Circuit
Turn ignition switch to OFF position. Measure resistance of BUS(-) circuit between PCM harness connector terminal No. 15 and DLC terminal No. 10. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in BUS(-) circuit to DLC. - Power Take-Off (PTO) Applications
If vehicle is equipped with PTO, go to next step. If vehicle is not equipped with PTO, replace PCM. - Check PTO On/Off Input
Turn ignition switch to ON position. On models equipped with 6.8L engine, while toggling PTO switch/actuator switch, measure voltage between breakout box pins No. 4 (PTO) and 51 or 103 (PWR GND). Voltage should be less than one volt with PTO off, and more than one volt with PTO on. If voltage is as specified, PTO circuit is okay. Replace PCM. If voltage is not as specified, perform TEST FB in appropriate SELF-DIAGNOSTICS article in ENGINE PERFORMANCE. - Check For BUS (+) Short To Bus (-)
Turn ignition switch to OFF position. Disconnect PCM 104-pin harness connector. Measure resistance between PCM harness connector terminals No. 15 BUS (-) and 16 BUS (+). If resistance is more than 5 ohms, go to next step. If resistance is less than 5 ohms, repair short circuit(s). - Check For Open BUS (+/-) In Harness
Measure resistance of BUS (+) Tan/Orange wire between PCM harness connector terminal No. 16 and DLC terminal No. 2. Measure resistance of BUS (-) Pink/Light Blue wire between PCM harness connector terminal No. 15 and DLC terminal No. 10. If both resistance readings are less than 5 ohms, repair module concern. See appropriate MODULE COMMUNICATIONS NETWORK article in ACCESSORIES & EQUIPMENT. If any resistance is 5 ohms or more, repair open in Pink/Light Blue wire or Tan/Orange wire.