P048

Code PO48 - Part 1 0f 2:

DTC PO48: Part 2 0f 2:

Emission Control Circuit:

CIRCUIT DESCRIPTION
This diagnostic test is designed to check for an Exhaust Gas Recirculation (EGR) system fault. After the engine is fully warmed up and the EGR system has been operating on full for a period of time, the Powertrain Control Module (PCM) will disable the EGR valve and monitor the change in rear short term fuel trim for the next 5 seconds. If the change is 14 counts or greater, the EGR system is functioning normally and will not be retested for the current ignition cycle. If the change is less than 14 counts, the test is failed and the counter is incremented. When the counter reaches 3, Code P048 is set. If at any time before the counter reaches 3 a change in the rear fuel integrator is 14 counts or greater the counter is decremented. If the counter reaches 0, the next rear short term fuel trim change of 14 counts or greater will pass the test for the entire ignition cycle. When Code PO48 is set, either the EGR system was turned off before the test started or the EGR system is functioning and the PCM does not have the ability to turn it off.

TEST CONDITIONS
1. EGR has not passed for the entire ignition cycle (refer to CIRCUIT DESCRIPTION).
2. Codes P013, P014, P015, P017, P021, P022, P031, P032, P034, P042, P043, P044, and P045 not set.
3. 10 minutes have passed since closed loop fuel control was enabled.
4. Engine coolant temperature between 80°C and 110°C.
5. Manifold Absolute Pressure (MAP) between 40 kPa and 75 kPa.
6. Engine speed between 1350 RPM and 2000 RPM.
7. Vehicle speed 35 mph or greater.
8. The following conditions present for 5 seconds prior to the test:

- EGR system on FULL.
- Rear oxygen sensor toggles 5 times per second.
- Rear short term fuel trim is 144 counts or less.

FAILURE CONDITIONS
1. PCM turns off EGR system for 5 seconds.
2. PCM monitors the rear short term fuel trim for a change.
3. Rear short term fuel trim change less than 14 counts; increment counter.
4. Counter reaches 3; set Code P048.

ACTION TAKEN
1. PCM turns "ON" the "Service Engine Soon" Malfunction Indicator Lamp (MIL).
2. PCM disables EGR system.

NOTES ON FAULT TREE
1. Checking for EGR operation using PCM override.

2. Checking for EGR gases to enter the intake manifold by raising the EGR valve off of its seat.

3. Checking for a EGR solenoid able to pass vacuum.

4. With engine idling, EGR solenoid should be energized. Test light across EGR solenoid terminals should be lit.

5. Checking for PCM's ability to turn solenoid "OFF."

NOTES ON INTERMITTENTS
At idle, manipulate the EGR solenoid connector and PCM connector and related wiring. The EGR solenoid should remain energized (CKT 435 grounded) to block vacuum to the EGR valve/vent vacuum to atmosphere. Listen for a change in idle quality.

Drive the car with Throttle Position (TP) sensor between 8 and 15 degrees and engine rpm at 1450 to 1650 RPM to try and duplicate the code.

With a hot engine (idling), apply and release vacuum to the EGR valve to check for EGR valve binding in the up or down position.

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 vacuum hoses for pinched, cut, kinked, misrouted, or hoses blocked.