coolblue65

I am trying to figure out what is wrong with my father's '01. It started misfiring so we pulled the codes and below is what we got: (we had the injectors all checked and they are all in perfect working condition) I have been looking through the service manuals with no luck yet.

Any thoughts on what direction I should take?

P0300 - The PCM has determined that multiple random misfires have occurred.

P0200 - The PCM has determined that a malfunction exists in the electrical circuit for the fuel injectors. - Definition: Fuel injector circuit condition. Explanation:The powertrain control module monitors for fuel injection circuit for opens, shorts & system overload conditions.
Probable causes:
1 - Open or shorted fuel injector
2 - Open or short in electrical circuit
3 - High fuel pressure - pressure regulator defective - fuel return line blocked
4- Check TPS and circuit for failure

Bill Dearborn

Don't know where you got the descriptions for those codes but they leave a little to be desired. You say are looking at the service manuals but I am attaching copies of the related diagnostics. A couple of things first.

Does your father have an aftermarket alarm system installed? GM has found that some of these systems cause misfires and cat damage. All alarms have to go through the starter circuit Vs the ignition circuits.

Here is a bulletin that GM sent out. It may be related.

97-05 Vehicles with 4.8 5.3 5.7 and 6.0 Gen III V8 Engines and Misfires on One Bank - kw CEL diagnostics driveability DTC P0171 P0172 P0174 P0175 P0300 P0301 P0302 P0303 P0304 P0305 P0306 P0307 P0308 #PIP3056 - (Jul 12, 2004)
97 - 05 Vehicles with 4.8 5.3 5.7 and 6.0 Gen III V8 Engines and Misfires On One Bank
.

The following diagnosis might be helpful if the vehicle exhibits the described symptoms in the PI.

Condition/Concern:
Check Engine Light with a P0300 due to 2 - 4 cylinders misfiring on the same bank of the engine. DTCs P0171, P0172, P0174 or P0175 may also set for the misfiring bank.

Recommendation/Instructions:
If the published misfire diagnostic does not isolate the cause, perform the following suggestions as necessary:

Perform a fuel injector balance test for all 8 cylinders. If a fuel injector concern exists, it is possible to misfuel an entire bank of the engine, causing multiple cylinders on the same bank to misfire even though the root cause is a single fuel injector.
Inspect O2 sensor connections on the misfiring bank for corrosion or water intrusion. If water intrusion is found on the right bank, it may be due to the AC Evaporator Condensation dripping onto the O2 sensor harness. If this condition is found, reposition and shield the harness to prevent a repeat concern and repair the connections.
Check for excessive exhaust backpressure using the restricted exhaust diagnosis from SI.
Swap the Position 1 O2 sensors side to side to see if the misfires move to the other bank of the engine. If so, replace the O2 sensor.
.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance.

Models:
(00 - 05 Cadillac Escalade - C6 and K6) and (02 - 05 Chevrolet Avalanche - C1, C2 K1 and K2) and (99 - 05 Chevrolet Silverado - C1, C2 K1 and K2) and (00 - 05 Chevrolet Suburban - C1, C2, K1 and K2) and (00 - 05 Chevrolet Tahoe - C1 and K1) and (99 - 05 GMC Sierra C1, C2 K1 and K2) and (00 - 05 GMC Yukon - C1, C2, K1 and K2) and (03 - 05 Chevrolet Express G1, G2, G3, H1, H2 ) and (03 - 05 GMC Savana G1, G2, G3, H1, H2 ) and (04 - 05 Buick Rainier S1, T1 ) and (03 - 05 Chevrolet Trail Blazer EXT S1, T1 ) and (03 - 05 GMC Envoy XL XUV S1, T1 ) and (03 - 05 Hummer H2) and (04 - 05 Cadillac CTS-V DB) and (98 - 02 Chevrolet Camaro FB) and (97 - 04 Chevrolet Corvette YB) and (98 - 02 Pontiac Firebird FB) and (04 - 05 Pontiac GTO VB)


Here is the diagnostic for P0300.
DTC P0300
System Description
The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensors and from the camshaft position (CMP) sensor in order to determine if engine misfire is occurring. By monitoring the variations in the crankshaft rotational speed for each cylinder, the PCM is able to detect individual cylinder misfire events. A misfire rate that is high enough can cause damage to the three-way catalytic converter (TWC). The malfunction indicator lamp (MIL) will flash if converter damage conditions are present.

Conditions for Running the DTC
DTCs P0101, P0102, P0103, P0117, P0118, P0125, P0335, P0336, P0341, P0342, P0343, P0500, P0502, P0503, P1120, P1220, P1221, or P1258 are not set.
The engine speed is between 425-3000 RPM.
The ignition voltage is between 10-18 volts.
The engine coolant temperature (ECT) is between -7°C-130°C (+19°F-266°F).
The fuel level is more than 10 percent.
The throttle angle is steady within 1 percent.
The anti-lock break system (ABS) and the traction control are not active.
The transmission is not changing gears.
The secondary air injection (AIR) diagnostic test is not in progress.
The A/C clutch is in a steady state.
The engine is not in fuel shut-off or in decel fuel cut-off.
The antilock brake system (ABS) signals are not exceeding the rough road thresholds.
Conditions for Setting the DTC
The PCM determines that an emission type misfire is present.
The PCM determines that a catalyst-damaging misfire is present.
Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
Conditions for Clearing the MIL/DTC
The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.
Diagnostic Aids

Important
Before you service the PCM and the throttle actuator control (TAC), remove any debris from the module connector surfaces. Inspect the module connector gaskets when you diagnose or replace the modules. Ensure that the gaskets are correctly installed. The gaskets prevent contaminate intrusion into the modules.
For any test that requires probing the PCM or probing a component harness connector, use the J 35616-A connector test adapter kit . Using this kit prevents damage to the harness and component terminals. Refer to Using Connector Test Adapters in Wiring Systems.

Running the vehicle out of fuel causes sufficient misfire to set DTC P0300. A vehicle that is out of fuel may have DTC P0461 and DTC P1431 also set.
A restricted fuel filter can cause sufficient misfire to set DTC P0300. Refer to Fuel System Diagnosis .
A misfire that only occurs during certain conditions may be difficult to locate. Observe the Freeze Frame and the Failure Records in order to determine when the DTC set.
Excessive vibration from sources other than the engine could cause a misfire DTC. Possible sources of vibration are listed below:
Variable thickness in the brake rotor
An unbalanced propeller shaft
Certain rough road conditions
If more than 1 cylinder is misfiring, the scan tool may only display 1 misfiring cylinder. This condition is not apparent until the repair is completed. Also, if an ignition coil or module ground circuit is open for 1 side of the engine, the scan tool may only display 2 or 3 misfiring cylinders. Inspect the ground circuit for the ignition coil and for the modules on the cylinder bank of the engine that has more than one misfiring cylinder.
A misfire may not be apparent at idle. The misfire may only occur above idle during a load. Road-test the vehicle, and monitor the misfire current counters.
For an intermittent condition, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.

2. The Misfire Current Counters will not increment if certain DTCs set at the same time or after DTC P0300 sets.

If more than 1 cylinder is misfiring, the Misfire Current Counters may increment for only one cylinder. For example, Cylinders 1 and Cylinder 8 are both misfiring, but only Cylinder 8 increments on the Misfire Current Counter.

If one of the injector fuses is open, only 2 or 3 Misfire Current Counters may increment for the corresponding side of the engine.

Wetting down the secondary ignition system with water from a spray bottle may help to locate damaged or deteriorated components. When you apply the water, look and listen for arcing or for misfiring.

If the Misfire Current Counters are incrementing and there is no apparent misfire, an erratic crankshaft position (CKP) sensor signal could be the cause. Perform the diagnostic that are listed on the table for DTC P0335 first if you suspect this condition.

If a misfire is present and you suspect a fuel control concern, force the fuel system into Open Loop using the scan tool, and allow the engine to run for a few minutes. If this procedure eliminates the misfire, refer to any fuel control-related DTCs which are set. If no other DTCs are set, refer to the Engine Scan Tool Data List.

4. The cylinder with the more significant misfire may cause another cylinder's counter to increment by a small amount.

10. If the engine misfire moves with the spark plug, this is good indication that you should replace the spark plug.

12. An engine mechanical condition can cause a spark plug to gas foul. Inspect for loose rockers, for collapsed lifters, or for worn camshaft lobes.

17. If the MIL is flashing, this indicates that a Catalyst Misfire has occurred. Drive the vehicle in the conditions to run the catalyst diagnostic.

DTC P0300 - Engine Misfire Detected Step
Action
Values
Yes
No

1
Did you perform Diagnostic System Check-Engine Controls?
--
Go to Step 2
Go to Diagnostic System Check - Engine Controls

2

Important
If any DTCs other than P0135 and P0155 are set, refer to those DTCs before proceeding with this diagnostic.


Install the scan tool.
Start the engine.
Use a scan tool in order to monitor all the Misfire Current Counters on the Misfire Data List. There are a total of 8 counters, with 1 counter per cylinder.
Are any of the Misfire Current Counters incrementing?
--
Go to Step 4
Go to Step 3

3
Turn ON the ignition, leaving the engine OFF.
Review the Freeze Frame and the Failure Records data for this DTC, and observe the parameters.
Turn OFF the ignition for 15 seconds.
Start the engine.
Operate the vehicle within the conditions required for this diagnostic to run, and as close as possible to the conditions that the Freeze Frame and Failure Records recorded. Special operating conditions that you need to meet before the PCM will run this diagnostic, where applicable, are listed in Conditions for Running the DTC.
Select the DTC option and the Specific DTC option, and then enter the DTC number using the scan tool.
Does the scan tool indicate that this diagnostic failed this ignition?
--
Go to Step 4
Go to Diagnostic Aids

4
Is only one Misfire counter incrementing?
--
Go to Step 6
Go to Step 5

5
Inspect for the following conditions:

Inspect the accessory drive belt and the pulleys for damage or for misalignment. Refer to Drive Belt Vibration Diagnosis in Engine Mechanical.
Inspect the vacuum hoses for splits, for kinks, and for proper connections.
Inspect the throttle body and the intake manifold for vacuum leaks.
Inspect the crankcase ventilation valve and system for vacuum leaks.
Inspect the PCM grounds for being clean and secure. Refer to Testing for Intermittent and Poor Connections in Wiring Systems .
Verify that all injector harness connectors are connected to the proper injector or cylinder.
Inspect the injector and the ignition control fuses for an open. If you find an open fuse, locate and repair the shorted circuit. Refer to Wiring Repairs in Wiring Systems.
Test for low fuel pressure or for restricted fuel flow. Refer to Fuel System Diagnosis .
Inspect for a restricted exhaust. Refer to Restricted Exhaust in Engine Exhaust.
Inspect the fuel for poor fuel quality. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
Did any of the above inspections isolate a condition requiring a repair?
--
Go to Step 17
Go to Step 6

6
Turn OFF the ignition.
Disconnect the injector that corresponds to the Misfire Current Counters that was incrementing.
Connect the injector test lamp J 34730-2C to the injector electrical connector.
Start the engine.
Is the injector test lamp flashing?
--
Go to Step 7
Go to DTC P0200

7
Turn OFF the ignition.
Reconnect the injector harness electrical connector.
Disconnect the ignition wires from the spark plug that corresponds to the Misfire Current Counters that was incrementing.
Install spark tester J 26792 to a ground.
Start the engine.
Does the spark jump the tester gap, and is the spark consistent?
--
Go to Step 9
Go to Step 8

8
Remove the ignition wire for the cylinder that is misfiring.
Use a DMM in order to measure the resistance of the ignition wire.
Is the ignition wire resistance less than the specified resistance?
700 ohms
Go to Electronic Ignition (EI) System Diagnosis
Go to Step 16

9
Remove the spark plugs from the cylinder that indicated a misfire.
Inspect the spark plugs. Refer to Spark Plug Replacement .
Does the spark plug appear OK?
--
Go to Step 10
Go to Step 11

10

Important
If the Injector Coil Test Procedure does not isolate the condition, refer to Base Engine Misfire without Internal Engine Noises in Engine Mechanical.


Swap the suspected spark plug with another cylinder that is operating properly.
Operate the vehicle under the same conditions in which the misfire occurred.
Did the misfire move with the spark plug?
--
Go to Step 15
Go to Fuel Injector Coil Test

11
Are the spark plugs oil or coolant fouled?
--
Go to Base Engine Misfire without Internal Engine Noises in Engine Mechanical
Go to Step 12

12

Important
If the Fuel System Diagnosis does not isolate the condition, refer to Base Engine Misfire without Internal Engine Noises in Engine Mechanical.


Are the spark plugs gas fouled?
--
Go to Fuel System Diagnosis
Go to Step 13

13

Important
If the Injector Coil Test Procedure does not isolate the condition, refer to Base Engine Misfire without Internal Engine Noises in Engine Mechanical.


Do the spark plugs show any signs of being cracked, worn, or improperly gapped?
--
Go to Step 14
Go to Fuel Injector Coil Test

14
Replace or re-gap spark plugs. If you find an improper gap, use a wire-type gauge in order to re-gap spark plugs. Refer to Spark Plug Replacement .

Did you complete the replacement?
--
Go to Step 17
--

15
Replace the faulty spark plugs. Refer to Spark Plug Replacement .

Did you complete the replacement?
--
Go to Step 17
--

16
Replace the faulty ignition wires. Refer to Spark Plug Wire Replacement .

Did you complete the replacement?
--
Go to Step 17
--

17
Was the MIL flashing?
--
Go to DTC P0420 or P0430
Go to Step 18

18
Use a scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC run and pass?
--
Go to Step 19
Go to Step 2

19
With a scan tool, observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?
--
Go to Diagnostic Trouble Code (DTC) List
System OK


Here is the diagnostic for P0200:

DTC P0200
Circuit Description
The control module enables the appropriate fuel injector on the intake stroke for each cylinder. Ignition voltage is supplied to the fuel injectors. The control module controls each fuel injector by grounding the control circuit via a solid state device called a driver. The control module monitors the status of each driver. If the control module detects an incorrect voltage for the commanded state of the driver, a fuel injector control DTC sets.

Conditions for Running the DTC
The engine speed is more than 400 RPM.
The ignition voltage is between 6-18 volts.
Conditions for Setting the DTC
The PCM detects an incorrect voltage on a fuel injector control circuit.
The condition exists for 5 seconds.
Action Taken When the DTC Sets
The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.
Conditions for Clearing the MIL/DTC
The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
Clear the MIL and the DTC with a scan tool.
Diagnostic Aids
Performing the Fuel Injector Coil test may help to isolate an intermittent condition. Refer to Fuel Injector Coil Test .
For an intermittent condition, refer to Intermittent Conditions .
Test Description
The numbers below refer to the step numbers on the diagnostic table.

4. This step tests for voltage at the fuel injector harness connector. The INJ fuse supplies power to the coil side of the fuel injector harness connector. If the fuse is open, a short to ground on the fuel injector B+ supply circuit is indicated. The INJ fuse also supplies voltage to the ignition coils. If the fuse is open, inspect the circuits to the ignition coils for a short to ground.

5. This step verifies that the PCM is able to control the fuel injector. If the test lamp blinks, then the PCM and the wiring are OK.

6. This step tests if a ground is constantly being applied to the fuel injector.

Fuel Injector Circuit Check Step
Action
Yes
No

Schematic Reference: Engine Controls Schematics

1
Did you perform the Diagnostic System Check-Engine Controls?
Go to Step 2
Go to Diagnostic System Check - Engine Controls

2
Use a scan tool in order to clear the DTCs.
Idle the engine at the normal operating temperature.
Use a scan tool in order to monitor the misfire current counters.
Are any of the misfire current counters incrementing?
Go to Step 4
Go to Step 3

3
Observe the Freeze Frame and/or Failure Records data for this DTC.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC, as specified in the supporting text or as close as possible to the Freeze Frame and/or Failure records data that you observed.
Does the DTC fail this ignition?
Go to Step 4
Go to Diagnostic Aids

4
Turn OFF the ignition.
Disconnect the appropriate harness connector of the fuel injector.
Turn ON the ignition, with the engine OFF.
Probe the ignition voltage circuit of the fuel injector with a test lamp connected to a good ground.
Does the test lamp illuminate?
Go to Step 5
Go to Step 11

5
Connect the fuel injector test lamp J 34730-2C between the control circuit and the ignition voltage circuit of the fuel injector harness connector.
Start the engine.
Does the test lamp blink?
Go to Step 9
Go to Step 6

6
Does the test lamp remain illuminated at all times?
Go to Step 8
Go to Step 7

7
Test the control circuit of the fuel injector for a short to voltage or for an open. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 14
Go to Step 10

8
Test the control circuit of the fuel injector for a short to ground. Refer to Circuit Testing and Wiring Repairs in Wiring Systems.

Did you find and correct the condition?
Go to Step 14
Go to Step 13

9
Inspect for poor connections at the harness connector of the fuel injector. Refer to Testing for Intermittent and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?
Go to Step 14
Go to Step 12

10
Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent and Poor Connections and Repairing Connector Terminals in Wiring Systems.

Did you find and correct the condition?
Go to Step 14
Go to Step 13

11

Important
The INJ fuse also supplies voltage to the ignition coil modules. If the fuse is open, inspect all related circuits for a short to ground.


Repair the ignition voltage circuit of the fuel injector for an open or for a short to ground. Refer to Wiring Repairs in Wiring Systems.

Did you complete the repair?
Go to Step 14
--

12
Replace the fuel injector. Refer to Fuel Injector Replacement .

Did you complete the replacement?
Go to Step 14
--

13
Replace the PCM. Refer to Powertrain Control Module (PCM) Replacement .

Did you complete the replacement?
Go to Step 14
--

14
Use a scan tool in order to clear the DTCs.
Turn OFF the ignition for 30 seconds.
Start the engine.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text.
Does the DTC run and pass?
Go to Step 15
Go to Step 2

15
Use a scan tool in order to observe the stored information, Capture Info.

Does the scan tool display any DTCs that you have not diagnosed?
Go to Diagnostic Trouble Code (DTC) List
System OK

Good Luck

Bill

coolblue65

Thanks for the quick reply, that info was from when my dad had the codes read (at Autozone), so I realize that they were pretty vague.

As far as your question about an aftermarket alarm, he does not have one.

That service bulletin is interesting because my father seems to ALWAYS have his AC on, so I will take a look at that along with check all wiring and related grounds.

I don't have a scan tool to help diagnose where exactly the misfire is coming from so it seems that advanced diagnose on my part might be pretty tough with out it.