Mechanics

CHEVY ENGINE BUCK UNDER LOW LOAD

2000 Chevrolet Silverado

Engine Performance problem
2000 Chevy Silverado V8 Four Wheel Drive Automatic 135000 miles

My Silverado is bucking when I slightly hold the gas around 55 mph. I recently had the fuel pump and filter changed. It is throwing code po449 (evaporative emission control vent/solenoid control circuit malfunction). If this is causing the bucking, how do I fix it?
Avatar
Bmahon723
November 19, 2008.



The bucking sounds more like an engine misfire. Check your plugs and wires for carbon tracking on the sides of the plugs. Below is a flow chart for the p0449 code.

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Service Information
2000 Chevrolet Chevy K Silverado - 4WD | Sierra, Silverado, Suburban, Tahoe, Yukon (VIN C/K) Service Manual | Document ID: 546856

DTC P0449 Evaporative Emission (EVAP) Vent Solenoid Control Circuit

Circuit Description
A voltage is supplied directly to the evaporative emission (EVAP) vent valve solenoid. The powertrain control module (PCM) controls the solenoid by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply the ground for the controlled component. Each driver has a fault line which the PCM monitors. The voltage of the control circuit should be low, near 0 volts, when the PCM commands a component ON. The voltage potential of the circuit should be high, near the battery voltage, when the PCM commands the control circuit to a component OFF. If the fault detection circuit senses a voltage other than what the PCM expects, the fault line status changes causing the DTC to set.

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 that the commanded state of the driver and the actual state of the control circuit do not match.

• The conditions are present for a minimum of 5 seconds.

Action Taken When the DTC Sets
• The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.

• The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the PCM stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the PCM records the operating conditions at the time of the failure. The PCM writes the conditions to the Freeze Frame and updates the Failure Records.

Conditions for Clearing the MIL/DTC
• The PCM turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.

• A last test failed, or current DTC, clears when the diagnostic runs and does not fail.

• A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.

• Use a scan tool in order to clear the MIL and the DTC.

Diagnostic Aids
Important: Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing or replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent water intrusion into the PCM.

Using Freeze Frame and Failure Records data may aid in locating an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and Failure Records data can aid in determining how many miles since the DTC set. The Fail Counter and Pass Counter can also aid in determining how many ignition cycles the diagnostic reported a pass or a fail. Operate the vehicle within the same Freeze Frame conditions, such as RPM, load, vehicle speed, temperature etc., that you observed. This will isolate when the DTC failed.

For an intermittent, refer to Symptoms .

Test Description
The numbers below refer to the step numbers on the diagnostic table.

Listen for an audible click when the solenoid operates. Be sure that both the ON and the OFF states are commanded. Repeat the commands as necessary.

This test can detect a partially shorted coil which would cause excessive current flow. Leaving the circuit energized for 2 minutes allows the coil to warm up. When warm the coil may open (amps drop to 0) or short (goes above 0.75 amp).

Momentarily probe the solenoid control circuit to ground. Listen for an audible click when the solenoid operates.

If no trouble is found in the control circuit or the connection at the PCM, the PCM may be faulty, however, this is an extremely unlikely failure.

Step
Action
Value(s)
Yes
No

1
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check ?
--
Go to Step 2
Go to Powertrain On Board Diagnostic (OBD) System Check

2
Turn ON the ignition, with the engine OFF.
Command the solenoid ON and OFF using the scan tool.
Does the solenoid turn ON and OFF when commanded?
--
Go to Step 3
Go to Step 5

3
Turn OFF the ignition.
Disconnect the PCM connector C2 located on the opposite side of the manufacturers logo. Refer to Powertrain Control Module Replacement .
Install 5 amp fused jumper wire to the control circuit at the PCM harness connector.
Turn ON the ignition, with the engine OFF.
IMPORTANT: Replace the solenoid if the current goes to 0 amps when performing the current draw test.

Measure the current from the solenoid control circuit in the PCM harness connector to ground for 2 minutes using the DMM on the 40 amp scale.
Does the current draw measure less than the specified value?
0.75 A
Go to Diagnostic Aids
Go to Step 4

4
Turn OFF the ignition.
Disconnect the solenoid.
Measure the resistance from the solenoid control circuit in the PCM harness using the DMM connected to ground. Refer to Testing for Continuity in Wiring Systems.
Does the DMM display infinite (OL) resistance?
--
Go to Step 14
Go to Step 15

5
Turn OFF the ignition.
Remove the underhood electrical center cover.
Remove the fender to cowl bracket.
Remove the underhood electrical center housing side shield.
Release and pivot the underhood electrical center up to gain access to the C152 connector, the 12 way Blue.
Disconnect the C152 connector.
Turn ON the ignition, with the engine OFF.
With the test lamp connected to B+, probe pin F on the male terminal connector.
Using the scan tool command the EVAP vent solenoid ON and OFF.
Does the test lamp illuminate each time the vent solenoid is commanded ON and OFF?
Go to Step 6
Go to Step 8

6
Reconnect the C152 connector.
Disconnect the solenoid.
Connect the test lamp between the terminals in the solenoid harness connector. Refer to Probing Electrical Connectors in Wiring Systems.
Turn ON the ignition, with the engine OFF.
Command the solenoid ON and OFF using the scan tool.
Does the test lamp turn ON and OFF when commanded?
Go to Step 9
Go to Step 7

7
With the test lamp connected to ground, probe the ignition feed circuit in the solenoid harness connector.

Is the test lamp illuminated?
--
Go to Step 12
Go to Step 13

8
Turn OFF the ignition.
Reconnect the C152 connector.
Disconnect the PCM connector C2 located on the opposite side of the manufacturer logo. Refer to Powertrain Control Module Replacement .
Turn ON the ignition, with the engine OFF.
With a fused jumper wire connected to ground, momentarily probe the solenoid control circuit in the PCM harness connector. Refer to Using Fused Jumper Wires in Wiring Systems.
Is there an audible solenoid click when the circuit is grounded and when the circuit is opened?
--
Go to Step 10
Go to Step 11

9
Inspect the connections at the solenoid. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
If you find a poor connection, repair the terminal as necessary. Refer to Connector Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 19
Go to Step 14

10
Inspect the connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
If you find a poor connection, repair the terminal as necessary. Refer to Connector Repairs in Wiring Systems.
Did you find and correct the condition?
--
Go to Step 19
Go to Step 18

11
Repair the faulty solenoid control circuit between the PCM and connector 152. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?
--
Go to Step 19
--

12
Repair the faulty solenoid control circuit between the solenoid and connector 152. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?
--
Go to Step 19
--

13
Repair the faulty solenoid ignition feed circuit. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?
--
Go to Step 19
--

14
Replace the solenoid. Refer to Evaporative Emission Vent Valve Replacement .

Is the action complete?
--
Go to Step 19
--

15
Turn OFF the ignition.
Remove the underhood electrical center cover.
Remove the fender to cowl bracket.
Remove the underhood electrical center housing side shield.
Lift the underhood electrical center up to gain access to the C152 connector, 12-way blue.
Disconnect the C152 connector.
Measure the resistance in the solenoid control circuit from the C152 connector male terminal pin F to ground.
Does the DMM display infinite resistance?
--
Go to Step 16
Go to Step 17

16
Repair the short to ground in the EVAP solenoid control circuit between the C152 connector and the EVAP solenoid. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?
--
Go to Step 19
--

17
Repair the short to ground in the EVAP solenoid control circuit between the PCM and the C152 connector. Refer to Wiring Repairs in Wiring Systems.

Is the action complete?
--
Go to Step 19
--

18
Important: The replacement PCM must be programmed.

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?
--
Go to Step 19
--

19
Select the Diagnostic Trouble Code (DTC) option and the Clear DTC Information option using the scan tool.
Idle the engine at the normal operating temperature.
Select the Diagnostic Trouble Code (DTC) option and the Specific DTC option, then enter the DTC number using the scan tool.
Operate the vehicle within the Conditions for Running the DTC as specified in the supporting text, if applicable.
Does the scan tool indicate that this test ran and passed?
--
Go to Step 20
Go to Step 2

20
Select the Capture Info option and the Review Info option using the scan tool.

Does the scan tool display any DTCs that you have not diagnosed?
--
Go to the applicable DTC table
System OK

© 2008 General Motors Corporation. All rights reserved.


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Dennyp
Nov 21, 2008.