Hesitation, Sag, Stumble

Definition: Momentary lack of response as the accelerator is pushed down. Can occur at any vehicle speed. Usually most pronounced when first trying to make the vehicle move, as from a stop sign. May cause the engine to stall if severe enough.

1. Was the "On-Board Diagnostic (OBD) System Check" performed?

[YES] Go to Step 2.
[NO] Go to OBD System Check. Initial Inspection

2. a. Perform a bulletin search.
b. If a bulletin that addresses the symptom is found, correct the condition as instructed in the bulletin.
c. Was a bulletin found that addresses the symptom?

[YES] Verify repair.
[NO] Go to Step 3.

3. Was a visual/physical check performed?

[YES] Go to Step 4.
[NO] Go to Visual/Physical Check. Visual/Physical Check

4. a. Check the fuel control Heated Oxygen Sensors (HO2S) (B1S1 and B2S1). The fuel control heated oxygen sensors (HO2S) should respond quickly to different throttle positions. If they don't, check them for silicon or other contaminants from fuel or use of improper RTV sealant. The sensors may have a white powdery coating. Silicon contamination causes a high but false HO2S signal voltage (rich exhaust indication). The [1][2]PCM will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem.
b. If a problem is found, repair as necessary.
c. Was a repair required?

[YES] Verify repair.
[NO] Go to Step 5.

5. a. Check the fuel pressure. Refer to Fuel System Pressure Test.
b. If a problem is found, repair as necessary.
c. Was a repair required?

[YES] Verify repair.
[NO] Go to Step 6.

6. a. Observe the Throttle Position (TP) angle display on the scan tool while slowly increasing throttle pedal.
b. Does the TP angle display steadily increase from 0% at closed throttle to 100% at Wide Open Throttle (WOT)?

[YES] Go to Step 7.
[NO] Go to Step 18.

7. Monitor "Long Term Fuel Trim on the scan tool. Is the "Long Term Fuel Trim" in the negative range (rich condition)?

[YES] Go to Step 8.
[NO] Go to Step 9.

8. a. Check items that can cause the engine to run rich. Refer to Diagnostic Aids in DTC P0172.
b. If a problem is found, repair as necessary.
c. Was a repair required?

[YES] Verify repair.
[NO] Go to Step 10.

9. a. Check items that can cause the engine to run lean. Refer to Diagnostic Aids in DTC P0171.
b. If a problem is found, repair as necessary.
c. Was a repair required?

[YES] Verify repair.
[NO] Go to Step 10.

10. a. Check for proper ignition voltage output with spark tester J 26792 (ST-125).
b. If a problem is found, repair as necessary.
c. Was a repair required?

[YES] Verify repair.
[NO] Go to Step 11.

11. a. Check for a loose ignition control module ground.
b. If a problem is found, repair as necessary.
c. Was a repair required?

[YES] Verify repair.
[NO] Go to Step 12.

12. a. Check the ignition coils for cracks or carbon tracking.
b. If a problem is found, repair as necessary.
c. Was a repair required?

[YES] Verify repair.
[NO] Go to Step 13.

13. a. Remove spark plugs and check for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits.

NOTE: If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs.

b. If a problem is found, repair as necessary.
c. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 14.

14. a. Check the Powertrain Control Module ([1][2]PCM) grounds for cleanliness, tightness and proper location. Refer to the PCM wiring diagrams.
b. If a problem is found, repair as necessary.
c. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 15.

15. a. Check the Mass Air Flow (MAF) sensor connections.
b. If a problem is found, replace the faulty terminals as necessary.
c. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 16.

16. a. Visually/physically check the vacuum hoses for splits, kinks, and proper connections and routing as shown on the "Vehicle Emission Control Information" label.
b. If a problem is found, repair as necessary.
c. Was a problem found?

[YES] Verify repair.
[NO] Go to Step 17.

17. a. Review all diagnostic procedures within this table.
b. If all procedures have been completed and no malfunctions have been found, review/inspect the following:
- Visual/physical inspection.
- Scan tool data.
- Freeze Frame data/Failure Records buffer.
- All electrical connections within a suspected circuit and/or system.
c. If a problem was found, repair as necessary.
d. Was a problem found?

[YES] Verify repair.
[NO] Contact Technical Assistance.

18. a. Replace the TP sensor.
b. Is the action complete?

[YES] Verify repair.