DFI CODE 13 AND 45 SET SIMULTANEOUSLY: DIAGNOSIS

MODELS AFFECTED: 1981-87 DE VILLE, ELDORADO AND SEVILLE EQUIPPED WITH THE HT4100 OR V8-6-4 ENGINE

Some 1981-87 De Villes, Broughams, Eldorados, and Sevilles equipped with an HT4100 or V8-6-4 engine may experience a condition of codes 13 and 45 setting simultaneously. These codes can set simultaneously when they occur in the following order:

o Code 45 sets when the oxygen sensor detects a rich exhaust signal.

o Then Code 13 sets when the oxygen sensor looses sensitivity due to prolonged operation under rich exhaust conditions.

To diagnose this condition, refer to the following "DFI Code 13 and Code 45" fault tree and notes.

Notes On Fault Tree: (Figure 1) -------------------------------

1. Disconnect O2 sensor, turn the ignition on and display engine data parameter O.7; it should be between .17 and .57 volts. If the oxygen sensor voltage reads greater than .57 volts with the sensor disconnected, check circuit #412 for a short to voltage. If the oxygen sensor voltage reads less than .37 volts, then check for a short to ground in circuit 412. If circuit 412 is okay, then check for a poor ground in circuit 413 and repair as necessary.

2. If the oxygen sensor voltage is between .37 and .57 volts install fuel pressure gage J-25400-300 at the fuel line service fitting. Measure the fuel pressure while cranking the engine; it should be between 9 and 12 psi. If the fuel pressure is less than 9 or greater than 12 psi, then see DFI Chart A-4, Fuel System Diagnosis in the appropriate Service Information Manual.

3. If the fuel pressure is between 9 and 12 psi check the fuel injector part numbers for proper application, per Bulletin 85-45. Should an incorrect injector be found, then replace it with a remanufactured unit as described in the Dealer Service Information Builetin 86-1-22.

4. If the injector part number is correct, record the MAP value (parameter O.2.) at a hot idle with the A/C off. If the MAP parameter is greater than 45 kPa, the ECM is seeing a low intake manifold vacuum. To verify this, "tee" a vacuum gage into the map hose at the throttle body and note intake vacuum. if intake vacuum exceeds 17 inches go to Step #5. if intake vacuum is less than 17 inches, perform the following:

A. Check for a leaking MAP sensor and/or hose -- disconnect the map hose from the TBI port and apply vacuum to the hose using a hand held vacuum pump with gage. The gage should hold vacuum, if it does not, replace the leaking hose or sensor.

B. Check for an obstruction under the EGR valve preventing the valve from seating properly.

C. Check for an intake manifold and/or gasket leak or engine mechanical condition causing low vacuum.

5. If the MAP parameter is less than 45 kPa perform a rich injector (stall) test as follows:

A. Set idle speed to minimum air idle. Disconnect the ISC motor connector.

B. Remove one fuel injector harness connector. Note engine stall.

C. Replace connector, restart engine and repeat with the other injector.

If the engine continues to run when one connector is removed, replace the injector which continues to run the car. If neither injector stalls the engine, then replace fuel meter assembly.

6. If both injectors stall the engine, then perform the following checks:

A. Check the evaporative emissions control canister for contamination or restrictions per Service Information Manual.

B. Remove the oxygen sensor and check for contamination, replace as necessary.

C. Check for signs of leaded or contaminated fuel.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.