Circuit Description
There should be a steady MIL with the ignition ON and the engine not running. Ignition feed voltage is supplied directly to the MIL bulb. The Powertrain Control Module (PCM) turns the MIL ON by grounding the MIL control circuit. No MIL with the key ON, engine not running and DTC P1641 set suggests an open in the MIL control circuit.
Diagnostic Aids
An intermittent may be caused by a poor connection, rubbed through wire insulation or a wire broken inside the insulation. Check the following items:
| • | Inspect the PCM harness and connectors for improper mating, broken locks, improperly formed or damaged terminals, poor terminal to wire connection, and damaged harness. |
| • | If the engine runs OK, check for a malfunctioning light bulb, an open in the MIL control circuit, or an open in the instrument cluster ignition feed. |
| • | If the engine cranks but will not run, check for an open PCM ignition or battery feed or a poor PCM to engine ground. |
Test Description
Numbers below refer to the Step numbers on the Diagnostic Table:
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A no MIL condition accompanied by a no start condition suggests a malfunctioning PCM ignition feed or battery feed circuit.
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Using a test lamp0 connected to B+, probe each of the PCM ground terminals to ensure that a good ground is present.
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This vehicle is equipped with a PCM which utilizes an Electrically Erasable Programmable Read Only Memory (EEPROM). When the PCM is being replaced, the new PCM must be programmed.
Step | Action | Values | Yes | No |
|---|---|---|---|---|
1 | Was the Powertrain On-Board Diagnostic (OBD) System Check performed? | -- | ||
Attempt to start the engine. Does the engine start? | -- | |||
3 | Check the fuse for the instrument cluster ignition feed circuit. Is the fuse OK? | -- | ||
4 |
Is the test lamp ON? | -- | ||
5 |
Is the MIL ON? | -- | ||
6 | Check the PCM ignition feed and battery feed fuses. Are both of the fuses OK? | -- | ||
7 |
Is the test lamp ON? | -- | ||
8 | Probe the battery feed circuit at the PCM harness connector with a test lamp to ground. Is the test lamp ON? | -- | ||
Was a problem found? | -- | |||
10 |
Was a problem found? | -- | ||
11 |
Was a problem found? | -- | ||
12 | Repair open in the ignition feed circuit to the instrument panel indicators. Refer to Wiring Repairs in Wiring Systems. Is action complete? | -- | -- | |
13 | Locate and repair open in PCM battery feed circuit or PCM ignition feed circuit as necessary. Refer to Wiring Repairs in Wiring Systems. Is action complete? | -- | -- | |
14 | Locate and repair short to ground in PCM ignition feed circuit or PCM battery feed circuit as necessary. Refer to Wiring Repairs in Wiring Systems. Is action complete? | -- | -- | |
15 | Locate and repair short to ground in the instrument panel indicators ignition feed circuit. Refer to Wiring Repairs in Wiring Systems. Is action complete? | -- | -- | |
|
Important:: The replacement PCM must be programmed. Replace the PCM. Refer to Powertrain Control Module Replacement/Programming . Is action complete? | -- | -- | ||
17 |
Was a problem found? | -- |
