Circuit Description
The powertrain relay is a normally open relay. The relay armature is held in the open position by spring tension. Battery positive voltage is supplied directly to the relay coil and the armature contact at all times. The powertrain control module (PCM) supplies the ground path to the relay coil control circuit, via an internal integrated circuit, called an output driver module (ODM). When the PCM commands the relay ON, the relay coil creates an electromagnetic field. This electromagnetic field overcomes the spring tension and pulls the armature contact into the stationary contact of the relay load circuit. The closing of the relay contacts allows the current to flow from the battery to the following fuses and relays:
| • | ETC fuse |
| • | Emission fuse |
| • | A/C relay |
| • | Air pump relay, if equipped |
When the ignition switch is turned to the OFF position, power is interrupted to the ODM in the PCM, and the relay electromagnetic field collapses. This action allows the spring tension pulling on the armature to separate from the relay load circuit contact, which interrupts current flow to the fuses and relays.
If the powertrain relay fails to close, the engine will crank, but will not run. The class 2 communications will be available with the use of a scan tool.
The powertrain relay system diagnosis table assumes that the vehicle battery is fully charged. Refer to Battery Inspection/Test in Engine Electrical.
Step | Action | Values | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Schematic Reference: Engine Controls Schematics and Power Distribution Schematics in Wiring Systems Connector End View Reference: Powertrain Control Module Connector End Views and Electrical Center Identification Views in Wiring Systems | ||||||||
1 | Did you perform the Diagnostic System Check - Vehicle? | -- | Go to Step 2 | Go to Diagnostic System Check - Vehicle in Vehicle DTC Information | ||||
2 | Attempt to start the engine. Does the engine start and run? | -- | Go to Intermittent Conditions | Go to Step 3 | ||||
3 |
Does the test lamp illuminate on at least one test point of each fuse? | -- | Go to Step 4 | Go to Step 13 | ||||
4 |
Does the test lamp illuminate on either test point of the fuse? | -- | Go to Step 5 | Go to Step 31 | ||||
5 |
Does the test lamp illuminate on either test points of the fuse? | -- | Go to Step 9 | Go to Step 6 | ||||
6 |
Notice: Refer to Test Probe Notice in the Preface section. Does the test lamp illuminate? | -- | Go to Step 7 | Go to Step 20 | ||||
7 |
Does the test lamp illuminate? | -- | Go to Step 26 | Go to Step 8 | ||||
8 | Test the powertrain relay coil control bus bar circuit in the underhood junction block for a short to ground. Refer to Circuit Testing in Wiring Systems. Did you find a condition? | -- | Go to Step 30 | Go to Step 25 | ||||
9 |
Does the test lamp illuminate on either test point of the fuse? | -- | Go to Step 10 | Go to Symptoms - Engine Electrical in Engine Electrical | ||||
10 |
Important: If vehicle is not equipped with an air pump relay, go to step 11. Does the test lamp illuminate on either test point of the fuse? | -- | Go to Step 11 | Go to Symptoms - Engine Electrical in Engine Electrical | ||||
11 |
Does the test lamp illuminate on either test point of the fuse? | -- | Go to Step 12 | Go to Symptoms - Engine Electrical in Engine Electrical | ||||
12 |
Notice: Refer to Test Probe Notice in the Preface section. Does the test lamp illuminate? | -- | Go to Step 30 | Go to Symptoms - Engine Electrical in Engine Electrical | ||||
13 |
Notice: Refer to Test Probe Notice in the Preface section. Does the test lamp illuminate? | -- | Go to Step 14 | Go to Step 18 | ||||
14 |
Does the test lamp illuminate? | -- | Go to Step 15 | Go to Step 18 | ||||
15 |
Does the test lamp illuminate? | -- | Go to Step 19 | Go to Step 16 | ||||
16 |
Does the resistance measure greater than the specified value? | 5 ohms | Go to Step 27 | Go to Step 17 | ||||
17 | Test the underhood junction block powertrain relay coil control bus bar circuit for a high resistance or an open. Refer to Circuit Testing in Wiring Systems. Does the resistance measure greater than the specified value? | 5 ohms | Go to Step 30 | Go to Step 25 | ||||
18 | Probe the mounting stud for the battery positive cable at the underhood junction block with a test lamp that is connected to a good ground. Does the test lamp illuminate? | -- | Go to Step 30 | Go to Symptoms - Engine Electrical in Engine Electrical | ||||
19 |
Does the test lamp illuminate on at least one test point of each fuse? | -- | Go to Step 20 | Go to Step 30 | ||||
20 | Measure the resistance from terminal #85 of the relay to terminal #86 with a DMM. Does the resistance measure within the specified value? | 70-110 ohms | Go to Step 21 | Go to Step 28 | ||||
21 | Measure the resistance from terminal #30 of the relay to terminal #87 with a DMM. Does the DMM display the specified value? | ∞ ohms | Go to Step 22 | Go to Step 28 | ||||
22 | Measure the resistance from terminal #30 of the relay to terminal #85 with a DMM. Does the DMM display the specified value? | ∞ ohms | Go to Step 23 | Go to Step 28 | ||||
23 | Measure the resistance from terminal #85 of the relay to terminal #87 with a DMM. Does the DMM display the specified value? | ∞ ohms | Go to Step 24 | Go to Step 28 | ||||
24 |
Does the resistance measure more than the specified value? | 3 ohms | Go to Step 28 | Go to Intermittent Conditions | ||||
25 | Test for shorted terminals and poor connections at the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and Micro-Pack 100W Connectors in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 31 | Go to Step 29 | ||||
26 | Repair the short to ground in the powertrain relay coil control circuit between the underhood junction block electrical connector and the PCM electrical connector. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 31 | -- | ||||
27 | Repair the high resistance or an open in the powertrain relay coil control circuit between the underhood junction block electrical connector and the PCM electrical connector. Refer to Wiring Repairs in Wiring Systems. Did you complete the repair? | -- | Go to Step 31 | -- | ||||
28 | Replace the powertrain relay. Refer to Relay Replacement in Wiring Systems. Did you complete the replacement? | -- | Go to Step 31 | -- | ||||
29 | Replace the PCM. Refer to Control Module References in Computer/Integrating Systems for replacement, setup, and programming. Did you complete the replacement? | -- | Go to Step 31 | -- | ||||
30 | Replace the underhood junction block. Did you complete the replacement? | -- | Go to Step 31 | -- | ||||
31 |
Does the engine start and run? | -- | Go to Step 32 | |||||
32 |
Does a DTC set during this ignition cycle? | -- | Go to Diagnostic Trouble Code (DTC) List - Vehicle in Vehicle DTC Information | System OK | ||||
