Action Taken

WARNING: This page is about a different car, the 1990 Cadillac Fleetwood and 1990 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.

ECM turns on SERVICE SOON light and locks on for entire key cycle.
EGR is disabled for entire key cycle.

Code E48 is designed to set if there is an EGR system fault. The test for Code E48 is performed under conditions where EGR is normally allowing exhaust gas to flow into intake.

To perform test, ECM turns off EGR flow to engine and monitors oxygen sensor (closed loop) integrator. With EGR turned off, integrator should swing to a higher value, reflecting leaner air/fuel mixtures. If not, ECM assumes either EGR was turned off before test started, or EGR is flowing and ECM does not have ability to turn it off.

NOTE: Test numbers refer to test numbers on diagnostic chart.

Test Number 1) Checks for EGR operation using ECM override.

Test Number 2) Checks for EGR gases to enter the intake manifold by raising the EGR valve off its seat.

Test Number 3) Checks for EGR solenoid vacuum flow.