E048

ECM Code E048:

ECM Code E048 (Cont'd):

DFI Emission Circuit:

DESCRIPTION:

To perform the test, the ECM (turns off EGR flow to the engine and monitors the oxygen sensor (closed loop) integrator. With EGR turned off, the integrator should swing to a higher value reflecting leaner air/fuel mixtures. If not, the ECM assumes that either EGR was turned off before the test started or that EGR is flowing and the ECM doesn't have the ability to turn it off. The ECM tests EGR six times in a given key cycle. If the EGR doesn't respond three or more times in five tests, code E048 is logged.

TEST CONDITIONS:

1. Codes EO13, EO14, EO15, E021, E022, E031, E032, E034, E044, E045 clear.
2. Coolant temp between 85° and 110°C.
3. TPS between 7° and 14°.
4. Engine speed between 1450 and 1650 RPM.
5. Oxygen sensor swinging (closed loop operation).
6. Vehicle speed greater than 35 MPH.
7. 10 minute timer after startup expired.
8. Steady throttle.

TEST:

During the above test conditions, the EGR system is normally enabled, allowing EGR to flow to the engine. The test that is performed is to turn OFF the EGR flow to the engine for five seconds and to monitor the closed loop integrator. With EGR flow turned OFF, the integrator value should increase by at least 14 counts; for example, the integrator might change from 130 counts to 144 counts or more to indicate that more fuel should be added to compensate for the leaner (less EGR) intake mixture. The ECM will perform the test no more than six times each key cycle; the ECM stops testing after three test failures are recorded.

FAILURE CONDITIONS:

If the oxygen sensor fails to indicate a leaner mixture in at least 3 of the 5 tests, code E048 is set.

ACTION TAKEN:

1. ECM turns on "SERVICE ENGINE SOON" telltale.
2. ECM commands BCM to display "SERVICE SOON" message on CCDIC.
3. EGR is disabled for the entire key cycle.

NOTES ON FAULT TREE:

1. Many codes disable EGR and inhibit the E048 test. Repair other DFI codes before diagnosis of code E048.

2. At idle, the EGR solenoid is electrically energized, blocking vacuum flow to the EGR valve.

NOTE ON INTERMITTENTS:

Drive the car at TPS between 8 and 15 degrees and engine speed at 1450 to 1650 RPM to try and duplicate the code. Remove the EGR valve and check for excessive carbon build up that would restrict EGR flow or foreign materials holding the EGR valve open. Check for blocked or restricted EGR passage in the intake manifold reducing EGR flow. Check vacuum hoses for pinched, cut, kinked, misrouted, or hoses blocked.

NOTES ON FAULT TREE:

1. Check for power at EGR solenoid.

2. Checking for the ability of the ECM to command EGR on.