4.0L L47 4.6L LD8 L37 Engine Intermittent Slow Speed Decel - kw decelerate DTC EGR IAC MIL PCM P1599 stall

When servicing the vehicle with the VIN you entered, the following diagnosis might be helpful if the vehicle exhibits the described symptoms.

Some1996-1999 Oldsmobile Aurora with the 4.0L(L47) and Cadillac vehicles with the 4.6L (LD8 L37) Northstar engine may exhibit an intermittent stall/near stall/idle flare or flux while the vehicle is at idle. The customer may not notice the near stall but, will notice the idle flare as the PCM tries to save the engine from stalling. Normally this condition will be accompanied with a PCM code P1599 for stall or near stall detected.

This condition of an intermittent slow speed decel stall may be caused by carbon deposits formed on the IAC and EGR valve or in the throttle body passages. If this vehicle stalls when coasting above speeds of 20 mph, one possible cause maybe the EGR valve sticking. (As with speeds above 20 mph the P0401 diagnostic will exercise the EGR valve to near 100% when certain conditions have been met.). The sticking condition may not be on the pintle end of the valve, but on the shaft; therefore cleaning the EGR valve may not improve this stall condition. It is important to note that the P0401 diagnostic does not seem to run when the Tech 2 is in the snapshot mode. This prevents a technician from seeing the condition as it occurs. If the answer to either of these questions is yes, then the condition is not the EGR sticking from the P0401 diagnostic.

1. Does the vehicle stall when coasting with the speed below 20 mph?
2. Can the condition be captured on the Tech 2 or VDR in the snapshot mode?

If the answer to either of the above questions is no, then the decel stall condition maybe caused due to EMI induced on the crank sensor ckt .This EMI originates from the #4 cylinder firing event, through the spark plug wire into the ICM (from the #4 coil/ICM proximity), which is then transferred into the sensor ckt due to the proximity of the icm to the sensor ckt.

1. Verify spark plug and wire resistances are not excessive. S/P resistance should be 5000 ohms +/- 2500 ohms at approx 68 degrees F. S/P wires should not exceed 3000 ohms per foot.
2. Verify PCM grounds by using a voltmeter to check the voltage drop (should not exceed 40 MV ).
3. Verify fuel pressure during condition.
4. Check for possible carbon deposits formed on the IAC and EGR or in the throttle body passages.
5. Verify the ICM ground.
6. Verify all 4 ICM connectors are secure.
7. Verify crank A, B and cam sensor connector pins are not bent and that they are seated correctly circuit integrity.
8. Verify crank A, B and cam sensors are free of metal shavings. The metal shavings could distort the signal from the sensors to the ICM and cause misinterpretation of the data.
9. If the above checks are good and the condition can be easily duplicated, then swap #1 AND #4 spark plug wires at the coil and evaluate. if the condition is eliminated and spark plug and wire resistance checks are good, then install a revised crankshaft position a sensor(top sensor) . If condition remains, then swap #6 AND #7 spark plug wires. If this eliminates the condition, and spark plug and wire resistance checks are good, then install the revised crankshaft position sensor in position B (bottom sensor). Also, if the condition can be duplicated easily, the problem can be verified by using the Tech 2 manual snapshot feature to monitor engine RPM and 4X reference( engine 2 data). If engine RPM drops to approx. 400 RPM and 4X ref drops below 8 (usually 5 or 6) or above 8 (usually 10), this will most likely be seen in frame -1 just before stall in frame 0 of your manual snap shot.

Please follow this diagnosis process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed. If these steps do not resolve the condition, please contact GM TAC for further diagnostic assistance. This diagnostic approach was developed for the vehicle with the VIN you entered and should not be automatically be used for other vehicles with similar symptoms.

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(96 -99 CADILLAC DEVILLE 4.6L (LD8) ENGINE ) and (96 -99 CADILLAC ELDORADO 4.6L (LD8, L37) ENGINE) and (96 -99 CADILLAC SEVILLE 4.6L (LD8, L37) ENGINE) and (96 -99 OLDSMOBILE AURORA 4.0L (L47) ENGINE )

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