Without Scan Tool

On-board Diagnostic System Check Operation Flow Chart:

ENTRY INTO DIAGNOSTICS
The Heater and Air Conditioning (H-A/C) control is used to display all of the vehicles' modules that will set a Diagnostic Trouble Code (DTC). Even though the CCM cannot display any other systems DTC's the "On-Board Diagnostic System Check" has been repeated here for the convenience of the reader.

If a fault is detected, there will be no flashing or any indication to the customer that an error has occurred, though he/she might detect a system malfunction. The system faults will be indicated and recorded in the diagnostic pointer numbers on page 8D- 10. When working on systems controlled by the CCM, the technician should always refer to this section and check for Diagnostic Trouble Codes (DTCs).

Diagnostics is entered through a two button simultaneous push by pressing the "OFF" button and the "TEMP" button. The mode of air delivery and blower functions will be preserved through the diagnostics entry process.

The immediate indication upon entry into diagnostics is that all enunciators, and display segments light for 5 seconds. The numerical display will then show the pointer number.O0. Refer to Page 8D-8 for an illustration of "entry into diagnostic display" and pointer-00.

To exit this diagnostic display mode the user must press any mode function key (except "OFF," "Rear Defog" or "Defog1,).

DIAGNOSTIC POINTERS
INPUTS/OUTPUTS

There are two types of display in this mode, a diagnostic pointer (indicated by a minus sign) which indicates what system you are looking at, or what Automatic Control Air Conditioning (ACAC) input/output (parameter) you are observing. The second type of display is the actual Diagnostic Trouble Code (DTC) that you are viewing for pointer selection 0.00 through 0.04.

The "Fan Up" and "Fan Down" keys will be used to increment and decrement, respectively, the diagnostic pointer number. There will be a wrap-around feature if the pointer umber. There will be a wrap-around feature if the pointer number sequence is continued past either end.

The "Out Temp" button will toggle the display between the diagnostic pointer number and the diagnostic trouble code/parameter. A "Fan Up"/"Fan Down" press while displaying the DTC will cause the display to show the pointer number.

In addition to CCM diagnostic trouble codes, the H-A/C control can also display Powertrain Control Module (PCM) Diagnostic Trouble Codes (DTCs),

Supplemental Inflatable Restraint (SIR) Diagnostic Trouble Codes (DTCs), Antilock Brake System/Traction Control (ABS/TCS) Diagnostic Trouble Codes (DTCs), and HVAC (ACAC) (DTCs).

CLEARING DTC'S
DTCs can be cleared from the H-A/C control while DTCs are displaying for the selected pointer being observed by pressing the "OFF" button. After DTCs are cleared, the display will show "00". The Tech 1 can also be used to clear DTCs.

Whenever the H-A/C control display shows - - this indicates the H-A/C control is not receiving serial data because of a fault on the serial data line to and including the H-A/C control.

INTERMITTENTS/HISTORY DTCs

History DTCs are those indicating that the CCM previously detected a fault which later disappeared. Any DTC that has a 1 as its first digit is a history DTC. Examples are: 120, 132, 137 etc. The reason could be either that the fault is a true intermittent, only happening occasionally, or that the system for which the DTC is not currently being operated. An example of this would be DTC 143 (key resistor circuit short to battery/open) CKT 1073 could have an intermittent short to B+. For this reason, if a DTC and operating the system that the DTC applies to. If the DTC resets, it can be assumed that the condition is present.

If a visual (physical) check does not find the cause of the problem, the vehicle can he driven with a DVM connected to the suspected circuit. An abnormal voltage or resistance reading when the problem occurs indicates the problem may be in that circuit.

In the case of the circuits which can be monitored by using the Tech 1 data display, these may be monitored for abnormal voltage, counts, etc. which occur at the same time the problem occurs, possibly indicating a problem with that circuit.

One example of this is DTC 22 changing from DTC 22 to DTC 122 while you are watching the Heater-A/C Control display. An intermittent short to B+ in CKT 1393 could cause the diagnostic display to alternate between DTC 22 and DTC 12.
All History DTCs will clear if there has been no faults for 50 ignition cycles.