THE DIAGNOSTIC PROCEDURE - WHERE TO START

TM 9-2320-364-20-1

Section IV. TROUBLESHOOTING CHARTS

A. THE DIAGNOSTIC PROCEDURE - WHERE TO START

When diagnosing the cause for engine performance, fuel economy or exhaust system complaints, perform Vehicle Trou-

bleshooting (Chapter 2) before considering DDEC as the possible source of the problem.

When diagnosing the system, always start with the first chart (labeled "START") on page 2-539. This will ultimately lead to

other diagnostic charts, even in the cases where no fault codes were logged but a symptom(s) was noted. In fact, if no

faults were recorded (but a symptom remains), the "START" chart will refer you to "Diagnosis by Symptom", Chart 1, on

page 2-554, which can identify fault trees to use based on the customer complaint.

NOTE:

Although there are many charts connected with diagnostics, only one is needed to determine that the

system is operating properly. Normally, only two charts are necessary to find a problem.

B. DDEC III/IV DIAGNOSTIC CODES/WHAT THEY MEAN

The following pages give a brief description of each diagnostic code. Basic facts about these codes are given below:

Most problems must occur for a total of at least two (2) seconds before the "Check Engine" light comes on and a code is

stored.

If a problem goes away, the "Check Engine" light will turn off. But the code will remain stored in the ECM.

Code 25 means no codes were stored at all.

FLASH CODE:

DDR DISPLAY:

PTO SENSOR (VERNIER CONTROL) INPUT VOLTAGE LOW

SAE J1587 CODE:

PID: 187 FMI: 4

Indicates that the vernier control input to the ECM has dropped below 5% (normally < 0.25 volts) of the sensor

supply voltage. This diagnostic condition is typically:

(1) open sensor signal circuit

(2) open sensor +5 volt supply circuit

(3) sensor signal is shorted to the sensor return circuit or to ground

(4) sensor +5 volt supply is shorted to sensor return circuit or to ground

FLASH CODE:

DDR DISPLAY:

PTO SENSOR (VERNIER CONTROL) INPUT VOLTAGE HIGH

SAE J1587 CODE:

PID: 187 FMI: 3

Indicates that the vernier control input to the ECM has exceeded 95% (normally > 4.75 volts) of the sensor supply

voltage. This diagnostic condition is typically:

(1) open sensor return circuit

(2) sensor signal circuit is shorted to the sensor +5 volt supply