| Table 1: | EFE Heater Relay Circuit |
Schematic Reference: Engine Controls Schematics
Circuit Description
The early fuel evaporation (EFE) heater provides a rapid heating of the air/fuel mixture during cold start conditions. Rapid heating provides quick fuel evaporation and more uniform fuel distribution. Rapid heating also reduces exhaust emission levels. The EFE heater is operated by a relay that is controlled by the powertrain control module (PCM). The EFE heater is a positive temperature coefficient design that is turned on when the engine is cold and running faster than 800 RPM. The PCM turns off the EFE relay when the engine reaches operating temperature or anytime the engine speed is reduced to idle.
Conditions for Running the DTC
| • | The engine is running. |
| • | Barometric pressure is greater than 75 kPa. |
| • | Intake air temperature is -10°C to 50°C (14°F to 122°F). |
Conditions for Setting the DTC
The EFE On Signal circuit voltage is less than 2.5 volts with the EFE heater ON.
OR
The EFE On Signal circuit voltage is greater than 0.3 volts with the EFE heater OFF.
Either condition is present for 5 seconds or more.
Action Taken When the DTC Sets
| • | The malfunction indicator lamp (MIL) illuminates after two consecutive ignition cycles in which the diagnostic runs with the fault active. |
| • | The PCM records the operating conditions at the time the diagnostic fails. This information will be stored in the Freeze Frame buffer. |
Conditions for Clearing the MIL/DTC
| • | The MIL turns OFF after three consecutively passing trips without a fault present. |
| • | A History DTC clears after 40 consecutive warm-up cycles without a fault. |
| • | Use the scan tool Clear DTC Information function or disconnect the PCM battery feed in order to clear the DTC. |
Diagnostic Aids
Check for any of the following conditions:
| • | Check the resistance of the EFE heater relay. The resistance across terminal 1 and terminal 2 is 79-95 ohms at 20°C (68°F). The resistance across terminal 3 and terminal 4 is infinite. |
| • | The EFE heater relay's electrical contacts may be pitted or sticking. Replace the EFE heater relay if tapping gently on the relay or wiggling the relay causes a change in the relay's operation. |
| • | The performance of the EFE heater relay may be affected by temperature. Check the EFE heater relay after sitting outside overnight and after running the engine 30 minutes. |
| • | Check for a faulty electrical connection to the PCM. |
An intermittent malfunction may be caused by a fault in the EFE heater electrical circuit. Inspect the wiring harness and components for any of the following conditions:
| • | Backed out terminals. |
| • | Improper mating of terminals. |
| • | Broken electrical connector locks. |
| • | Improperly formed or damaged terminals. |
| • | Faulty terminal to wire connections. |
| • | Physical damage to the wiring harness. |
| • | A broken wire inside the insulation. |
| • | Corrosion of electrical connections, splices, or terminals. |
If a DTC P1250 cannot be duplicated, the information included in the Freeze Frame data can be useful in determining vehicle operating conditions when the DTC was first set.
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.
Relay Cavity Identification | |
|---|---|
Switch Power | |
Switch Load | |
Coil Power | Coil Ground |
Test Description
The numbers below refer to the step numbers in the Diagnostic Table.
-
The Powertrain OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.
-
This step will verify whether the EFE heater relay circuit is always ON. The EFE heater relay should only be grounded when the engine is running and the ECT sensor is reading less than 80°C (176°F).
-
This step will verify whether the PCM is providing a ground path for the EFE heater relay circuit. Terminal 2 of the EFE heater relay is grounded by the PCM only when the engine is running and the ECT sensor is reading less than 80°C (176°F).
Step | Action | Value(s) | Yes | No | ||||
|---|---|---|---|---|---|---|---|---|
Did you perform the Powertrain On-Board Diagnostic (OBD) System Check? | -- | |||||||
2 | Check for an open in the PTC fuse. Was an open fuse found? | -- | ||||||
3 |
Does the test lamp illuminate? | -- | ||||||
4 | Probe terminal 1 of the EFE heater relay (relay box side) using a test lamp connected to ground. Does the test lamp illuminate? | -- | ||||||
Does the test lamp illuminate? | -- | |||||||
Did the test lamp illuminate? | 75°C (167°F) | |||||||
7 |
Is the action complete? | -- | -- | |||||
8 |
Was a repair necessary? | -- | ||||||
9 |
Was a repair necessary? | -- | ||||||
10 |
Was a repair necessary? | -- | ||||||
11 |
Does the test lamp illuminate? | 75°C (167°F) | ||||||
12 | Measure the resistance of the EFE Heater with a DMM. Is the EFE heater resistance within the specified value? | 0.5-3.0 ohms at 20°C (68°F) | ||||||
13 |
Was a repair necessary? | -- | ||||||
14 |
Was a repair necessary? | -- | ||||||
15 | Repair the short to ground in the PTC fuse circuit. Refer to Wiring Repairs in Wiring Systems. Is the action complete? | -- | -- | |||||
16 |
Was a repair necessary? | -- | ||||||
17 | Replace the EFE heater. Refer to EFE Heater Replacement . Is the action complete? | -- | -- | |||||
18 | Replace the EFE heater relay. Refer to EFE Heater Relay Replacement . Is the action complete? | -- | -- | |||||
19 | Replace the PCM. Refer to Powertrain Control Module Replacement . Is the action complete? | -- | -- | |||||
20 | Operate the vehicle within the conditions under which the original concern was noted. Does the system operate properly with no DTCs? | -- | System OK | Go to the Applicable Diagnostic Table |
