Suburban 3/4 Ton 4WD V8-305 5.0L (1986)
ECM Replacement Check for Chart C-1
CHART C-1 - ECM REPLACEMENT CHECK
Circuit Description:
Prior to replacing an ECM, the circuit involved must be tested for:
^
Poor connector terminal to ECM contact;
^
Direct battery voltage on an ECM ground circuit from a short to B+; or
^
Shorted solenoid or relay. If a short is found, the circuit must be repaired prior to replacing the ECM to prevent repeat ECM failures
Test Description:
1.
Check for good terminal contact due to weak or dirty terminals. Remove terminal to inspect. Replace if broken or dirty. If coolant is present, replace
coolant sensor and connector. Also, replace ECM connector terminal and blow coolant out of harness. Clean connector with alcohol or spray
contact cleaner and replace ECM.
2.
Check for a short to ignition or shorted solenoid or relay. All terminals must be tested since several are connected internally in the ECM. A short in
one circuit may cause another circuit in the ECM to be inoperative that does not have an external fault, but was the cause of "driver's complaint."
Any circuit testing below 20 ohms is shorted to ignition, or shorted across the relay or solenoid.
3.
Check for shorted TCC solenoid. Some transmissions have a normally open 4th gear switch in series with the solenoid. The ohmmeter will read
infinite resistance (open circuit) in these cases. If the reading is less than 20 ohms, a short to ignition or faulty solenoid exists. A normal solenoid
will read between 20 - 50 ohms.
4.
Check for shorted TCC circuit in units with a 4th gear switch. The vehicle must be in 4th gear to close the switch to obtain a resistance reading. A
normal solenoid will read between 20-50 ohms.
Checking Control Module For Bad Solder Joints
Some control module's may have problems due to cracked solder joints on the circuit board. These internal control module problems can cause the
following symptoms:
^
Failure to start or vehicle is stalling.
^
The "CHECK ENGINE" "SERVICE ENGINE SOON" or "MALFUNCTION INDICATOR" light will flash or light up, but no trouble codes
will be present.
^
Vehicle instrument panel displays may be inoperative.
^
The control module may or may not communicate with the scanner.
^
Other intermittent driveability problems.
Incorrect PROM or MEMCAL removal and replacement can create solder joint problems or aggravate an existing condition. See PROM or
MEMCAL INSTALLATION for proper procedures.
