GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Geo 🢒 1997 🢒 Prizm 🢒 Engine 🢒 Engine Controls - 1.8L 🢒 Malfunction Indicator Lamp (MIL) Inoperative
Table 1: EFI Relay Circuit

Schematic Reference: Refer to Engine Controls Schematics

Circuit Description

There should always be a steady Malfunction Indicator Lamp (MIL) when the ignition switch is in the ON position and the engine is not running. System voltage is applied to the indicator bulb. The Powertrain Control Module (PCM) will control the MIL and turn it ON by providing a path to ground.

Diagnostic Aids

Check EFI F-HTR, IGN and GAUGE fuses for opens and make sure the EFI relay is securely mounted into the fuse and relay box.

If the EFI fuse opens (blows) during cranking, check for a shorted fuel pump/circuit. The EFI relay supplies power to the circuit opening relay which in-turn powers the fuel pump. The circuit opening relay is energized during cranking and when reference pulses are monitored by the PCM.

An intermittent malfunction may be caused by a poor connection, rubbed through wire insulation, or a wire broken inside the insulation. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals and poor terminal-to-wire connections before component replacement.

Use the following relay cavity table in order to locate the correct cavities to probe during diagnosis. The table layout corresponds to the cavity layout of the relay block.

EFI Relay Circuit

Relay Cavity Identification

Switch Load

Switch Power

Coil Power

Coil Ground

Test Description

The numbers below refer to the step numbers in the Diagnostic Table.

  1. If other ICA functions are not working correctly check for an open GAUGE fuse or for a lack of power and ground to the ICA.

    2.

  2. This step checks for an open MIL Control circuit or for an internal PCM failure.

    3.

  3. If the MIL does NOT illuminate when jumpered to ground, the failure is internal to the ICA.

  4. This step checks for an open EFI Relay.

    5.

  5. This step checks for open PCM ground circuits.

    6.

  6. A shorted sensor reference voltage circuit may cause a no start and no MIL condition.

Step

Action

Value

Yes

No

1

Did you perform the Powertrain On-Board Diagnostic (OBD) System Check?

--

Go to Step 2

Go to Powertrain On Board Diagnostic (OBD) System Check

2

Attempt to start and idle the engine.

Does the engine start?

--

Go to Step 3

Go to Step 6

3

Observe Instrument Cluster Assembly (ICA) operation.

Do all other functions of the ICA function normally?

--

Go to Step 4

Go to ICA Diagnosis in Instrument Panel, Gages and Console

4

  1. Turn OFF the ignition switch.
  2. Disconnect PCM electrical connector C1.
  3. Turn ON the ignition, leaving the engine OFF.
  4. Probe the MIL control circuit (harness side) with a fused jumper to ground.

Does the MIL illuminate?

--

Go to Step 21

Go to Step 5

5

  1. Turn ON the ignition, leaving the engine OFF.
  2. Backprobe Instrument Cluster Assembly (ICA) electrical connector C2 terminal 10 with a fused jumper wire to ground.

Does the MIL illuminate?

--

Go to Step 14

Go to ICA Diagnosis in Instrument Panel, Gages and Console

6
  1. Inspect the GAUGE fuse (Junction Block 1) for the following:
    2. • An open condition (blown fuse)
    • No ignition positive voltage supply
  2. Repair any of the above conditions as necessary. Refer to Wiring Repairs in Wiring System.

Was a repair necessary?

--

Go to Step 22

Go to Step 7

7
  1. Remove the EFI Relay.
  2. Probe the relay switch power terminal with a test lamp connected to ground. Refer to the Relay Cavity Identification table in Diagnostic Aids.

Does the test lamp illuminate?

--

Go to Step 8

Go to Step 15

8
  1. Turn ON the ignition, leaving the engine OFF.
  2. Probe the relay coil power terminal with a test lamp connected to ground.

Does the test lamp illuminate?

--

Go to Step 9

Go to Step 16

9

Connect the test lamp across the relay coil power and coil ground terminals.

Does the test lamp illuminate?

--

Go to Step 10

Go to Step 17

10

  1. Connect a fused jumper between the relay switch power terminal and the switch load terminal.
  2. Attempt to start and idle the engine.

Does the engine start?

--

Go to Step 18

Go to Step 11

11
  1. Turn OFF the ignition switch.
  2. Remove the fused jumper.
  3. Install the EFI Relay.
  4. Disconnect all PCM connectors.
  5. Turn ON the ignition switch.
  6. Probe PCM connector C1 terminal 12 with a test lamp connected to ground.

Does the test lamp illuminate?

--

Go to Step 12

Go to Step 19

12

Probe the PCM ground circuit terminals with a test lamp connected to B+.

Does the test lamp illuminate on all terminals?

--

Go to Step 13

Go to Step 20

13

  1. Check the manifold absolute pressure (MAP) sensor and the throttle position (TP) sensor REFERENCE voltage circuits for a short to ground. Check that the sensors are not internally shorted.
  2. Repair faults in the circuits as necessary. Refer to Wiring Repairs in Wiring System.

Was a repair necessary?

--

Go to Step 22

Go to Step 21

14

Repair the open in the MIL control circuit. Refer to Wiring Repairs in Wiring System.

Is the action complete?

--

Go to Step 22

--

15

Repair the open circuit between the EFI fuse and the EFI Relay. Refer to Wiring Repairs in Wiring System.

Is the action complete?

--

Go to Step 22

--

16

Repair the open circuit between the IGN fuse and the EFI Relay. Refer to Wiring Repairs in Wiring System.

Is the action complete?

--

Go to Step 22

--

17

Repair the open circuit in the EFI Relay ground circuit. Refer to Wiring Repairs in Wiring System.

Is the action complete?

--

Go to Step 22

--

18

Replace the EFI Relay.

Is the action complete?

--

Go to Step 22

--

19

Repair the open circuit between the EFI Relay and the PCM. Refer to Wiring Repairs in Wiring System.

Is the action complete?

--

Go to Step 22

--

20

Repair the open circuits between the PCM and ground. Refer to Wiring Repairs in Wiring System.

Is the action complete?

--

Go to Step 22

--

21

Replace the PCM. Refer to Powertrain Control Module Replacement .

Is the action complete?

--

Go to Step 22

--

22

Turn ON the ignition, leaving the engine OFF.

Is the MIL illuminated?

--

Go to Step 23

Go to Step 2

23
  1. Perform the scan tool Clear DTC Information function.
  2. Start the engine.

Observe the MIL operation.

Is the MIL illuminated?

--

Go to Engine Controls Schematics

System OK