MIL ON, DTC Code 34 Set
86amcjeep02APRIL 1986 000 906
1985-1986 CHEROKEE/ WAGONEER MODELS WITH CALIFORNIA V-6 AND MANUAL TRANS.
13E
ENGINE Attention: Workshop, Parts Department
DIAGNOSTIC CODE 34 FLASHING (Vacuum Sensor Circuit)
Some 1985 and 1986 Jeep Cherokee and Wagoneer vehicles equipped with a California V-6 engine (Fuel Feedback) and manual transmission may encounter a Diagnostic Code 34 flashing from the CHECK ENGINE light on the instrument panel.
Diagnostic Code 34 indicates that the vacuum sensor circuit has a voltage outside of its normal range. This circuit includes the vacuum sensor, connector, harness, and the ECU.
Refer to Diagnostic Code 34 Diagnostic Chart on page B-309 of MR 244.
If diagnosis does not indicate a condition requiring service, then the ECU calibration PROM may be sending a false signal to the CHECK ENGINE light.
To correct this false display from Diagnostic Code 34, the ECU calibration PROM must be replaced. The diagnostic and replacement procedures are outlined below.
DIAGNOSTIC PROCEDURE
The self-diagnostic system detects the conditions most likely to occur. The diagnostic system illuminates the CHECK ENGINE light in the instrument panel when need for service is detected.
Fig. 1 - Diagnostic Code Tester:
When a jumper wire is connected between diagnostic code test terminals No. 6 and No. 7 of the 15-terminal diagnostic connector (D-2) the CHECK ENGINE light will flash a code or codes that indicate the area(s) which may need service (Fig. 1).
For a bulb and system check, the CHECK ENGINE light will illuminate when the ignition switch is on and the engine not started.
If the test terminals are then grounded, the light will flash a Code 12. This indicates the selfdiagnostic system is operational.
A Code 12 consists of:
A. One flash, followed by a
B. Short pause; then, C. Two flashes in quick succession;
D. Then, after a longer pause, the code will repeat two (2) more times.
When the engine is started, the CHECK ENGINE light will remain on momentarily and then turn off. If the CHECK ENGINE light remains on, the self-diagnostic system has detected a problem. If the test terminals are then grounded, the diagnostic code will flash three
(3) times.
The diagnostic codes will flash in numeric order (lowest number code first). The code series will repeat as long as the test terminals are grounded.
Fig. 2 - ECU:
REPLACEMENT PROCEDURE
1. Disconnect the positive battery cable.
2. Remove the ECU from the vehicle. The ECU is located under the instrument panel to the right of the steering column.
3. Remove the metal access cover (A) from the ECU. This is accomplished by removing the two retaining screws (B) (Fig. 2).
4. Remove the PROM from the ECU circuit board.
CAUTION: Be careful not to bend the pins while pulling the PROM out of the ECU.
5. Install the replacement PROM (C), P/N 8953 004 807, (Fig. 2).
NOTE: The replacement PROM is contained in a plastic holder. This plastic holder is keyed to prevent reverse installation of the PROM.
6. Properly place the PROM (C) on the circuit board.
CAUTION: Be sure to align the key for the correct installation.
7. Press down on the PROM to fully insert it into the circuit board.
8. Install the access cover (A) and retaining screws (B).
9. Install the ECU in the vehicle.
10. Connect the positive battery cable.
11. Road test the vehicle.
PARTS INFORMATION
DESCRIPTION QUANTITY PART NUMBER
PROM, ECU Calibration 1 8953 004 807
SRT/TIC INFORMATION
OPERATION
OPERATION DESCRIPTION NUMBER TIME TIC
CO. PROM, ECU - REPLACE 0105 0.5 1 -356***
***SUPPLIER CODE: 602
FILING INSTRUCTIONS
Record this information on page B-290 and B-309 and file in the July, 1985 edition of M.R. 244 workshop manual.