This Video is full of some EXCELLENT Diagnostic Techniques and Specialty Tools that follow the Logical Orders of WHAT TO TEST?….1,st, 2nd, 3rd...Etc., when Investigating a No Communication Problem with the ECU-PCM. I’ve isolated and documented all of the critical information shown in this Video that follow the Proper Diagnostic 'Step By Steps' as a Written Reference Guide to compliment the Video:
The Vehicle:
2008 Chevrolet Silverado 5.3L
The Problem:
No Crank – No Start
The Diagnostic Tools:
The Mechanic’s Expertise in Digital Diagnostics
SnapOn Scan Tool
OBD2 (16) LED Digital DLC Break-Out Box
DMM Features on the Scan Tool (Voltmeter, Ammeter)
“Scope-On-A-Rope” Light Probe
Red/Black Wired “Pin Probes”
Wire “Puncture” Probe Adapter (ALWAYS Apply Liquid Electrical Tape on ALL Wire Punctures!)
Starter Diagnostics:
Jumpered the Starter Relay to confirm that the Starter Turns Over. It Worked Okay.
PCM Ground Wire Diagnostics using a “Graduated Eye-Ball, Hands and Fingers:
The Mechanic examined the Ground Wire located at the Front Passenger Side Engine Head where there is a “Beefy Nut On A Stud” and was looking for anything obviously LOOSE with the Ground Cable. However, the contacts were good and solid with No Frayed or Corroded Wires in evidence.
GM Class 2 Network Integrity Test using a DMM and a DLC Break Out OBD2 Test Tool:
The Mechanic’s next move was to “Break Out...The DLC Break-Out Box” (See Link at the Bottom of this Thread for Possible Choices) that Interfaces the Common OBD2 Female Port under the Driver’s Side of the Dashboard. Using his Meter Red & BLACK Probes while connecting the various Wire Pairs of from the OBD2 Interface, he was able to visualize the Network Integrity after observing the Uniquely Colored (16) LED Bulbs on the Break-Out Tool. Meanwhile, as he made these Pairings... he was also using his Scan Tool set to read Ohms. With his knowledge that the CAN System uses a Pair of 120 Ohm Resistors (One of those Resistors resides inside of the ECM-PCM)… He was able to check and confirm that the pairs of connections noted below that displayed at around 60 Ohms for these Connections; a Definitive Confirmation that the Network Wiring Integrity was Sound:
First... Ensure that the Ignition Key is in the OFF Position… As the Class 2 Network NEEDS to GO TO SLEEP
Note: Whenever (2) Resistors of the Same Value are Wired in Parallel on the Same Circuit ...the Ohms Value will become ½ of the Value of ONE of those Two Resistors… so ½ * 120 Ohms = 60 Ohms. This Test showed as (+) Lead at Pin (6) CAN HIGH and (-) Lead at Pin (14) CAN LOW ...Reading a Proper (60) Ohms. An Alternative Method for Testing the OBD2 Class 2 Network Wiring Integrity is to Set your DMM to Read Volts DC and continuing to use the DLC Break Out Box… Plug In:
(-) Black Lead at Pin (4) then the (+) Red Lead to Pin (6) and if the Network is GOOD, you should be seeing 2.5 – 2.6 Volts DC. THEN Move the (+) Red Lead over to Pin (14) and you should be seeing 2.2 Volts DC or near that Voltage Range if then Network Integrity is Sound and has No Broken or Wires Shorted to Ground. The Ohms Test is the More Reliable Method of these two to use for this Network Integrity Test.
Checking the ECM-PCM Fuses at the Under-Hood PDC (Power Distribution Center)
Next , The Mechanic Pulls the Cover from the PDC and using his “Scope-On-A-Rope” Power Probe expecting to see a Nice, Bright Light in the Probe Handle if these Circuits are operational. First… he probes FUSE # 56 (Key ON→ HOT in RUN or START). Next he tests FUSE # 12 (HOT AT ALL TIMES) for the power on the ECM-PCM Battery Fused Circuit… Then FUSE # 4 for the Power Train Relay Control...which showed NO LIGHT….and therefore No PCM Control over the Power Control Relay...Strongly Indicating a FAILED ECM-PCM Unit... ALTHOUGH... I wonder why he did NOT Consider Testing or Replacing the PCR Relay, as well?
Searching for a (5) Volt Reference Signal from the PCM @ Various Modules Under Hood & Dash
Using the DMM Voltmeter setting on his Scan Tool, The Mechanic next unplugs the MAP Sensor Connector and with the Key ON, Back-Probes the GRAY Wire, looking to see approximately (5) Volts DC on his DMM Voltmeter (Confirmed). Next, he likewise Back-Probes the MAF Sensor at the TAN-BLACK Wire for the IAT Voltage seeking the same (5) Volts DC on his DMM Voltmeter (Confirmed). The Last search for (5) Volts DC is done under the Dash at the Accelerator Pedal while Back-Probing the Two Middle WHITE/BLACK and TAN Wires for the HIGH and LOW Reference Voltages and likewise, he found and Confirmed the presence of (5) Volts DC there as well.
Performing a PCM Voltage Drop Test via Back-Probing the PCM at the TOP Harness Connector
The Mechanic’s needed to Check for Battery Voltage 12.5 to 13+ VDC or any Voltage Drops that occur right at the ECM-PCM The focus is on the TOP Harness Connector after removing the Outer Protective Plastic Wire Harness Shield. He attempts to Probe the PINK Wire at Pin (19) then the RED w/ WHITE STRIP Wire at Pin (20) as well as the Big BLACK Ground Wire at the Far Right Side of the Connector, which he confirmed as a Good Ground being well under 100 mV at around 11 mV. While attempting to Probe the RED w/WHITE STRIPE Wire and the PINK Wire… he had to resort to using a Piercing Probe after isolating that Wire along the outside area down from the Connector inside the looser Wire Bundle. Both display the proper DC Voltage of a Battery on a Charger of around 14 Volts.
The Mechanic removed the Connector to make a visual inspection searching the Plastic Wire Pin Slots for anything unusual or corroded inside and uses a “Drag Test Tool” using a properly sized “Terminal Cleaning Tool” but failed to be able to clean out the affected internal Pin Points for the aforementioned two Hot 12 VDC Wires or clean out their innards and pathways for better connectivity. At that point, he Declared The Problem to be: A “Dead PCM” ...at least in its inability to Communicate on the Class 2 Network, anyway.
A New ECM-PCM was Ordered, Installed and Programmed;
The Mechanic installed a New ECM-PCM for this 08’ Silverado and then hooked up the OBD2 Port to a J-2534 Unit acting as a PASS-THRU Device via his Laptop Computer in order to Re-Program the New PCM via a TIS2WEB Update with the Correct Truck VIN. He also performed a Security Re-Learn for Both Owner Ignition Keys as well as conducting the requisite CASE Re-Learn as well.
Here are some possible choices to consider if you want to obtain an OBD2 DLC Break-Out Box Tool:
https://www.amazon.com/s?k=dlc+breakout+tool&ref=nb_sb_noss&tag=elightbars-20
The Vehicle:
2008 Chevrolet Silverado 5.3L
The Problem:
No Crank – No Start
The Diagnostic Tools:
The Mechanic’s Expertise in Digital Diagnostics
SnapOn Scan Tool
OBD2 (16) LED Digital DLC Break-Out Box
DMM Features on the Scan Tool (Voltmeter, Ammeter)
“Scope-On-A-Rope” Light Probe
Red/Black Wired “Pin Probes”
Wire “Puncture” Probe Adapter (ALWAYS Apply Liquid Electrical Tape on ALL Wire Punctures!)
Starter Diagnostics:
Jumpered the Starter Relay to confirm that the Starter Turns Over. It Worked Okay.
PCM Ground Wire Diagnostics using a “Graduated Eye-Ball, Hands and Fingers:
The Mechanic examined the Ground Wire located at the Front Passenger Side Engine Head where there is a “Beefy Nut On A Stud” and was looking for anything obviously LOOSE with the Ground Cable. However, the contacts were good and solid with No Frayed or Corroded Wires in evidence.
GM Class 2 Network Integrity Test using a DMM and a DLC Break Out OBD2 Test Tool:
The Mechanic’s next move was to “Break Out...The DLC Break-Out Box” (See Link at the Bottom of this Thread for Possible Choices) that Interfaces the Common OBD2 Female Port under the Driver’s Side of the Dashboard. Using his Meter Red & BLACK Probes while connecting the various Wire Pairs of from the OBD2 Interface, he was able to visualize the Network Integrity after observing the Uniquely Colored (16) LED Bulbs on the Break-Out Tool. Meanwhile, as he made these Pairings... he was also using his Scan Tool set to read Ohms. With his knowledge that the CAN System uses a Pair of 120 Ohm Resistors (One of those Resistors resides inside of the ECM-PCM)… He was able to check and confirm that the pairs of connections noted below that displayed at around 60 Ohms for these Connections; a Definitive Confirmation that the Network Wiring Integrity was Sound:
First... Ensure that the Ignition Key is in the OFF Position… As the Class 2 Network NEEDS to GO TO SLEEP
Note: Whenever (2) Resistors of the Same Value are Wired in Parallel on the Same Circuit ...the Ohms Value will become ½ of the Value of ONE of those Two Resistors… so ½ * 120 Ohms = 60 Ohms. This Test showed as (+) Lead at Pin (6) CAN HIGH and (-) Lead at Pin (14) CAN LOW ...Reading a Proper (60) Ohms. An Alternative Method for Testing the OBD2 Class 2 Network Wiring Integrity is to Set your DMM to Read Volts DC and continuing to use the DLC Break Out Box… Plug In:
(-) Black Lead at Pin (4) then the (+) Red Lead to Pin (6) and if the Network is GOOD, you should be seeing 2.5 – 2.6 Volts DC. THEN Move the (+) Red Lead over to Pin (14) and you should be seeing 2.2 Volts DC or near that Voltage Range if then Network Integrity is Sound and has No Broken or Wires Shorted to Ground. The Ohms Test is the More Reliable Method of these two to use for this Network Integrity Test.
Checking the ECM-PCM Fuses at the Under-Hood PDC (Power Distribution Center)
Next , The Mechanic Pulls the Cover from the PDC and using his “Scope-On-A-Rope” Power Probe expecting to see a Nice, Bright Light in the Probe Handle if these Circuits are operational. First… he probes FUSE # 56 (Key ON→ HOT in RUN or START). Next he tests FUSE # 12 (HOT AT ALL TIMES) for the power on the ECM-PCM Battery Fused Circuit… Then FUSE # 4 for the Power Train Relay Control...which showed NO LIGHT….and therefore No PCM Control over the Power Control Relay...Strongly Indicating a FAILED ECM-PCM Unit... ALTHOUGH... I wonder why he did NOT Consider Testing or Replacing the PCR Relay, as well?
Searching for a (5) Volt Reference Signal from the PCM @ Various Modules Under Hood & Dash
Using the DMM Voltmeter setting on his Scan Tool, The Mechanic next unplugs the MAP Sensor Connector and with the Key ON, Back-Probes the GRAY Wire, looking to see approximately (5) Volts DC on his DMM Voltmeter (Confirmed). Next, he likewise Back-Probes the MAF Sensor at the TAN-BLACK Wire for the IAT Voltage seeking the same (5) Volts DC on his DMM Voltmeter (Confirmed). The Last search for (5) Volts DC is done under the Dash at the Accelerator Pedal while Back-Probing the Two Middle WHITE/BLACK and TAN Wires for the HIGH and LOW Reference Voltages and likewise, he found and Confirmed the presence of (5) Volts DC there as well.
Performing a PCM Voltage Drop Test via Back-Probing the PCM at the TOP Harness Connector
The Mechanic’s needed to Check for Battery Voltage 12.5 to 13+ VDC or any Voltage Drops that occur right at the ECM-PCM The focus is on the TOP Harness Connector after removing the Outer Protective Plastic Wire Harness Shield. He attempts to Probe the PINK Wire at Pin (19) then the RED w/ WHITE STRIP Wire at Pin (20) as well as the Big BLACK Ground Wire at the Far Right Side of the Connector, which he confirmed as a Good Ground being well under 100 mV at around 11 mV. While attempting to Probe the RED w/WHITE STRIPE Wire and the PINK Wire… he had to resort to using a Piercing Probe after isolating that Wire along the outside area down from the Connector inside the looser Wire Bundle. Both display the proper DC Voltage of a Battery on a Charger of around 14 Volts.
The Mechanic removed the Connector to make a visual inspection searching the Plastic Wire Pin Slots for anything unusual or corroded inside and uses a “Drag Test Tool” using a properly sized “Terminal Cleaning Tool” but failed to be able to clean out the affected internal Pin Points for the aforementioned two Hot 12 VDC Wires or clean out their innards and pathways for better connectivity. At that point, he Declared The Problem to be: A “Dead PCM” ...at least in its inability to Communicate on the Class 2 Network, anyway.
A New ECM-PCM was Ordered, Installed and Programmed;
The Mechanic installed a New ECM-PCM for this 08’ Silverado and then hooked up the OBD2 Port to a J-2534 Unit acting as a PASS-THRU Device via his Laptop Computer in order to Re-Program the New PCM via a TIS2WEB Update with the Correct Truck VIN. He also performed a Security Re-Learn for Both Owner Ignition Keys as well as conducting the requisite CASE Re-Learn as well.
Here are some possible choices to consider if you want to obtain an OBD2 DLC Break-Out Box Tool:
https://www.amazon.com/s?k=dlc+breakout+tool&ref=nb_sb_noss&tag=elightbars-20
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