ECM REPLACEMENT CHECK CHART
In order to reduce incidents of repeat ECM failure, a revised ECM diagnostic procedure is available. Beginning in 1982, most ECMs are equipped with Integrated Circuits (IC) in place of separate transistors to operate various controlled components.
These ICs, called Quad-Drivers (QDR), have 4 separate outputs, meaning that each QDR can operate up to 4 different components. An inoperative QDR can result in ECM output becoming open or shorted to ground. Often, all 4 outputs of a QDR will fail, even if just one QDR circuit is faulty.
Refer to the following tables to determine which ECMs contain QDRs. Since this procedure is not applicable to ECMs which do not contain QDRs, those ECMs are not listed.
Performing the diagnostic flow chart will identify an inoperative QDR. Once the circuit is identified, it must be repaired to eliminate repeat ECM failure. This diagnostic procedure must be used when "Replace ECM" is the conclusion of any procedure.
| Application | Output Terminals | ||
|---|---|---|---|
| 1984-85 | |||
| 1226458, 1226460 | |||
| QDR No. 1 | C1, C2, A2, A3 | ||
| QDR No. 2 | A4, A5, A7, A7 | ||
ECM QDR IDENTIFICATION
| Application | Output Terminals | ||
|---|---|---|---|
| 1983-84 | |||
| 1226153, 1226452, 12266454, 1226455. 1226519 | |||
| QDR No. 1 | G, E, 6, 4 | ||
| QDR No. 2 | 8, 19, P, P | ||
| QDR No. 3 | 18, 18, T, T | ||
| 1985-87 | |||
| 226457, 1226519, 1226865, 1226866, 1227076 | |||
| 1227169, 1227301, 1227855, 1228079 | |||
| QDR No. 1 | G, E, 6, 4 | ||
| QDR No. 2 | 8, 19, P, P | ||
| QDR No. 3 | 18, 18, T, T | ||
ECM QDR IDENTIFICATION
| Application | Output Terminals | ||
|---|---|---|---|
| 1984-85 | |||
| 1226461 | |||
| QDR No. 1 | A2, A4, A4, A5 | ||
| QDR No. 2 | A3, A3, D2, D2 | ||
| QDR No. 3 | A7, A7, C2 | ||
| 1985-87 | |||
| 1226869, 1226870, 1226948, 1227065, 1227784 | |||
| QDR No. 1 | A2, A4, A4, A5 | ||
| QDR No. 2 | A3, A3, D2, D2 | ||
| QDR No. 3 | C2, A7, A7 | ||
| 1986 | |||
| 1227151 | |||
| QDR No. 1 | C1, C2, A2, A3 | ||
| QDR No. 2 | A4, A5, A7, A7 | ||
| 1986-87 | |||
| 1227153, 1227170, 1227302 | |||
| QDR No. 1 | A2, A4, A4, A5 | ||
| QDR No. 2 | A3, A3, D2, D2 | ||
| QDR No. 3 | A7, A7, C2 | ||
| 1227165 | |||
| QDR No. 1 | A3, A7, C2, D12 | ||
| QDR No. 2 | A2, A4, A5, C1 | ||
| 1985-87 | |||
| 1226459 | |||
| QDR No. 1 | A3, A3, D3, D3 | ||
| QDR No. 2 | A7, A7, D2 | ||
| QDR No. 3 | A2, A4, A4, A5 | ||
| 1227730 | |||
| QDR No. 1 | E7, E8, E9, F7 | ||
| QDR No. 2 | F1, F2, F3, F4 | ||
| QDR No. 3 | F5, F5, F6, F8 | ||
| 1986-87 | |||
| 1227057 | |||
| QDR No. 1 | A3, A7, D2, D3 | ||
| QDR No. 2 | A4, A5, B2, B9 | ||
| 1227148, 1227783, 1227886 | |||
| QDR No. 1 | A3, A3, D3, D3 | ||
| QDR No. 2 | A7, A7, A8, D2 | ||
| QDR No. 3 | A2, A4, A4, A5 | ||
| 1987 | |||
| 1227750 | |||
| QDR No. 1 | 2A1, 2A8, 2A10, 2A11 | ||
| QDR No. 2 | 3C7, 3C8, 3C9, 3C10 | ||
| QDR No. 3 | 3D5, 3D5, 3D4, 3C6 | ||
| QDR No. 4 | 3C4, 3C4, 3C5, 3D4 | ||
ECM QDR IDENTIFICATION
| Application | (1) Output Terminals | ||
|---|---|---|---|
| 1983-87 | |||
| 1225610, 1226100, 1226026, 1226430 | |||
| QDR No. 1 | Black 9, Black 14, Black 16, White 20 | ||
| QDR No. 2 | Black 7, Black 22, White 19, White 19 | ||
| 1226026, 1226430 | |||
| QDR No. 1 | Black 9, Black 14, Black 16, White 20 | ||
| QDR No. 2 | Black 7, Black 22, White 19, White 19 | ||
| 1226156 | |||
| QDR No. 1 | White 20, Black 7, Black 9 | ||
| 1226864 | |||
| QDR No. 1 | Black 7, Black 9, White 20 | ||
| 1226867 | |||
| QDR No. 1 | A2, A3, A4, C2 | ||
| QDR No. 2 | C1, A5, A7, A7 | ||
| 1226868, 1227746, 1227747 | |||
| QDR No. 1 | A2, A3, C1, C2 | ||
| QDR No. 2 | A4, A5, A7, A7 | ||
| 1227137, 1227429 | |||
| QDR No. 1 | A2, A3, C1, C2 | ||
| QDR No. 2 | A4, A5, A7, A7 | ||
| 1227748 | |||
| QDR No. 1 | Black 7, Black 7, Black 18, White 18 | ||
| QDR No. 2 | Black 3, Black 4, White 21, White 22 | ||
| 1227749 | |||
| QDR No. 1 | E7, E8, E9, F7 | ||
| QDR No. 2 | F1, F2, F3, F4 | ||
| (1) Colors refer to ECM connector colors. | |||
| (1) | Colors refer to ECM connector colors. |
ECM QDR IDENTIFICATION
| Application | (1) Output Terminals | ||
|---|---|---|---|
| 1983-86 | |||
| 1226028, 1226462, 1226930 | |||
| QDR No. 1 | Blue 9, Blue 14, Blue 16, Red 20 | ||
| QDR No. 2 | Blue 7, Blue 22, Red 19, Red 19 | ||
| 1986-87 | |||
| 1227056 | |||
| QDR No. 1 | A7, A7, A11, A11 | ||
| QDR No. 2 | A2, A5, C3, C3 | ||
| QDR No. 3 | C1, D2, D3, D10 | ||
| QDR No. 4 | A3, A3, A4, A4 | ||
| (1) Colors refer to ECM connector colors. | |||
| (1) | Colors refer to ECM connector colors. |
ECM QDR IDENTIFICATION
Note. Use this chart only after the normal diagnostic charts have determined that there is an ECM failure.
ECM Replacement Check Chart C-1. Scheme 146
Scheme 147
The P/N switch contacts are closed to ground in Park or Neutral, and open in all Drive ranges. The ECM supplies ignition voltage, through a current limiting resistor, to circuit No. 434. The ECM senses a closed switch when voltage on circuit No. 434 drops to less than one volt. The ECM uses P/N signal as one of the inputs to control idle air, VSS diagnostics, and EGR flow.
Note. Test numbers refer to test numbers on diagnostic chart.
- Checks for closed switch to ground in Park position. Different makes of "SCAN" tools will read P/N signal differently. Refer to tool's instruction manual for type of display used for specific Tool.
- Checks for an open switch in Drive or Reverse.
- Be sure "SCAN" tool indicates Drive, even while wiggling shifter, to test for an intermittent or misadjusted switch in Drive.
If circuit No. 434 indicates P/N switch grounded while in Drive, EGR would be inoperative, resulting in possible detonation.
If circuit No. 434 always indicates Drive (open), a drop in idle may exist when gear selector is moved into Drive.
Park/Neutral Switch Diagnosis ("SCAN" Diagnosis). Scheme 148
The crank signal is a 12-volt signal to the ECM during cranking to allow enrichment, and to cancel diagnostics until engine is running, or 12 volts on circuit is no longer present.
Note. Test numbers refer to test numbers on diagnostic chart.
- Checks for normal (cranking) voltage to terminal "C9" of ECM. Test light should be on during cranking and then go off when engine is running.
- Checks to determine if source of open fuse or fuse link was a faulty ECM.
Crank Signal Diagnosis. Scheme 149
The power steering pressure switch is normally open to ground, and circuit No. 495 will be near battery voltage. Turning steering wheel increases power steering oil pressure, and its load on an idling engine. The pressure switch will close before the load can cause an idle problem. Closing switch causes circuit No. 495 to read less than one volt. The ECM will increase idle air rate and retard timing.
Note. Test numbers refer to test numbers on diagnostic chart.
- Checks for ECM signal voltage on circuit No. 495, and confirms ground circuit No. 450 is okay.
- Maximum resistance, or infinity, indicates an open switch.
- Less than one ohm indicates that switch is closed when power steering pressure is high. Switch is okay.
A pressure switch that will not close, or an open circuit No. 495 or circuit No. 450, may cause the engine to stop when power steering loads are high.
A switch that will not open, or a circuit No. 450 or circuit No. 495 shorted to ground, will cause timing to retard at idle, and may affect idle quality.
Power Steering Pressure Switch (2.5L). Scheme 150
The ECM control of the A/C clutch improves idle quality and performance by delaying clutch application until idle air rate is increased, releasing clutch when idle speed is too low, releasing clutch at wide open throttle, and smoothing cycling of compressor by providing additional fuel at instant clutch is applied.
Turning on A/C supplies circuit No. 459 battery voltage to the clutch control relay and terminal "B8" of ECM connector. After a time delay of about .5 second, the ECM will ground terminal "A4" (circuit No. 458), and close the control relay. A/C compressor clutch will engage.
Note. Test numbers refer to test numbers on diagnostic chart.
- Checks for low refrigerant as cause for no A/C.
- This and following tests check for faulty A/C control relay.
- Checks for faulty cycling switch. Solenoids and relays are turned on and off by the ECM, using internal electronic switches (drivers). Each driver is part of a group of 4, called "Quad-Drivers". Failure of one driver can damage any other driver in set. Solenoid and relay coil resistance must measure more than 20 ohms. Less resistance will cause early failure of ECM driver. Using an ohmmeter, check coil resistance of A/C relay before replacing ECM.
Before replacing ECM, use ohmmeter to check resistance of each ECM-controlled relay or solenoid. Replace any relay or solenoid that measures less than 20 ohms.
A/C Clutch Control Diagnosis Schematic (2.5L). Scheme 151
A/C Clutch Control Diagnosis Flow Chart (1 of 2) (2.5L). Scheme 152
A/C Clutch Control Diagnosis Flow Chart (2.5L) (1 of 2). Scheme 153
A/C Clutch Control Diagnosis Flow Chart (2 of 2) (2.5L). Scheme 154
From A/C Clutch Control Diagnosis Chart (1 Of 2). Scheme 155
The ECM control of the A/C clutch improves idle quality and performance by delaying clutch application until idle air rate is increased, releasing clutch when idle speed is too low, releasing clutch at wide open throttle, and smoothing cycling of compressor by providing additional fuel at instant clutch is applied.
Turning on A/C supplies circuit No. 59 battery voltage to the clutch control relay and terminal "B8" of ECM connector. After a time delay of about .5 second, the ECM will ground terminal "A2" (circuit No. 459), and close the control relay. A/C compressor clutch will engage.
Note. Test numbers refer to test numbers on diagnostic chart.
- Checks for low refrigerant as cause for no A/C.
- This and following tests check for faulty A/C control relay.
- Checks for faulty cycling switch. Solenoids and relays are turned on and off by the ECM, using internal electronic switches (drivers). Each driver is part of a group of 4, called "Quad-Drivers". Failure of one driver can damage any other driver in set. Solenoid and relay coil resistance must measure more than 20 ohms. Less resistance will cause early failure of ECM driver. Using an ohmmeter, check coil resistance of A/C relay before replacing ECM.
Before replacing ECM, use ohmmeter to check resistance of each ECM-controlled relay or solenoid. Replace any relay or solenoid that measures less than 20 ohms.
