ODBII - Trouble Codes
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ODBII - Trouble Codes - 12/7/2006 2:03:14 PM
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Hanr3
Wheels & Tire Moderator
Posts: 3479
Joined: 5/11/2005
Status: offline
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How the Diagnostic Trouble Code is created: A DTC is made up of 5 digits. The chart below shows the composition of a DTC. With this information you can easily determine what system to trouble shoot without knowing the exact description of the code.
X X X X X
The 1st X:
B- Body
C- Chassis
P- Powertrain
U- Network
2nd X:
0- SAE
1-MFG
3rd X
1- Fuel & Air Metering
2- Fuel & Air Metering (Injector)
3- Ignition System or Misfire
4- Auxiliary Emission Controls
5- Vehicle Speed & Idle Control System
6- Computer Output Citcuit
7- Transmission
8- Transmission
9- Reserved
0- Reserved
The last 2X are for the specific fault.
A complete driving cycle will perform diagnostics on all monitored systems and can usually be completed in less than fifteen minutes.
Performing a GM OBDII Driving cycle:
Cold Start. In order to be classified as a cold start the engine coolant temperature must be below 122°F (50°C) and within 11°F (6°C) of the ambient air temperature at startup. Do not leave the key on prior to the cold start or the heated oxygen sensor diagnostic may not run.
Idle. The engine must be run for two and a half minutes with the air conditioner on and rear defroster on. The more electrical load you can apply the better. This will test the O2 heater, Passive Air, Purge "No Flow", Misfire and if closed loop is achieved, Fuel Trim.
Accelerate. Turn off the air conditioner and all the other loads and apply half throttle until 55mph (88km/hr) is reached. During this time the Misfire, Fuel Trim, and Purge Flow diagnostics will be performed.
Hold Steady Speed. Hold a steady speed of 55mph (88km/hr) for 3 minutes. During this time the O2 response, air Intrusive, EGR, Purge, Misfire, and Fuel Trim diagnostics will be performed.
Decelerate. Let off the accelerator pedal. Do not shift, touch the brake or clutch. It is important to let the vehicle coast along gradually slowing down to 20 mph (32km/hr). During this time the EGR, Purge and Fuel Trim diagnostics will be performed.
Accelerate. Accelerate at 3/4 throttle until 55-60mph (88-96 km/hr). This will perform the same diagnostics as in step 3.
Hold Steady Speed. Hold a steady speed of 55mph (88km/hr) for five minutes. During this time, in addition to the diagnostics performed in step 4, the catalyst monitor diagnostics will be performed. If the catalyst is marginal or the battery has been disconnected, it may take 5 complete driving cycles to determine the state of the catalyst.
Decelerate. This will perform the same diagnostics as in step 5. Again, don't press the clutch or brakes or shift gears.
There are two categories of DTC's that apply to OBDII.
Type A
Emissions related.
Requests illumination of the MIL after one failed driving cycle.
Stores a freeze frame DTC after one failed driving cycle.
Type B
Emissions related.
Sets a Pending Trouble Code after one failed driving cycle.
Clears a Pending Trouble Code after one successful driving cycle.
Turns on the MIL after two consecutive failed driving cycles.
Stores a freeze frame after two consecutive failed driving cycles.
_____________________________
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'87 S10-Blazer - SOLD
'93 S10-Blazer 4x4x4 - Sons DD, engine swap is done.
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