Circuit Description
The fuel level sensor changes resistance based on fuel level. The PCM monitors the signal circuit of the fuel level sensor in order to determine fuel level. When the fuel tank is full, the sensor resistance is high and the PCM senses a high signal voltage. When the fuel tank is empty, the sensor resistance is low and the PCM senses a low signal voltage. The PCM uses the signal circuit of the fuel level sensor in order to calculate the total remaining fuel (%) in the tank. The PCM sends the fuel level percent via the class 2 serial data circuit to the instrument cluster in order to control the fuel gage. The fuel level information is also used for misfire and EVAP diagnostics.
Conditions for Running the DTC
The ignition is ON.
Conditions for Setting the DTC
| • | The fuel level Sensor signal is approximately 0.4 volts. |
| • | The above condition is present for greater than 10 seconds. |
Action Taken When the DTC Sets
| • | The fuel gage defaults to empty. |
| • | The low fuel indicator illuminates, and the audible warning sounds. |
| • | The PCM records the operating conditions at the time the diagnostic fails. The PCM displays the failure information in the Failure Records on the scan tool. |
Conditions for Clearing the DTC
| • | The DTC becomes history when the conditions for setting the DTC are no longer present. |
| • | The history DTC clears after 40 malfunction free warm-up cycles. |
| • | The PCM receives the clear code command from the scan tool. |
Diagnostic Aids
Use the Freeze Frame and/or Failure Records data in order to locate an intermittent condition. If you cannot duplicate the DTC, the information included in the Freeze Frame and/or Failure Records data may aid in determining the number of miles since the DTC set. The Fail Counter and Pass Counter can also aid in determining the number of ignition cycles that the diagnostic reported a pass and/or fail. Operate the vehicle within the same freeze frame conditions (RPM, engine load, vehicle speed, temperature, etc.). This will isolate when the DTC failed.
Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
Test Description
The number below refers to the step number on the diagnostic table.
Step | Action | Value(s) | Yes | No |
|---|---|---|---|---|
Schematic Reference: Instrument Cluster Schematics | ||||
1 | Did you perform the Instrument Cluster Diagnostic System Check? | -- | Go to Step 2 | |
2 |
Does the scan tool indicate that the Fuel Level Sensor parameter is less than the specified value? | 0.4 V | Go to Step 3 | Go to Diagnostic Aids |
3 | Is DTC P1635 current in the PCM? | -- | Go to DTC P1635 in Engine Controls | Go to Step 4 |
Does the scan tool indicate that the Fuel Level Sensor parameter is greater than the specified value? | 4.9 V | Go to Step 6 | Go to Step 5 | |
5 | Test the signal circuit of the fuel level sensor for a short to ground. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 8 |
6 | Test the signal circuit of the fuel level sensor for a short to ground between C420 and the fuel level sensor. Refer to Circuit Testing and to Wiring Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 7 |
7 | Inspect for poor connections at the harness connector of the fuel level sensor. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 9 |
8 | Inspect for poor connections at the harness connector of the PCM. Refer to Testing for Intermittent Conditions and Poor Connections and to Connector Repairs in Wiring Systems. Did you find and correct the condition? | -- | Go to Step 11 | Go to Step 10 |
9 | Replace the fuel level sensor. Refer to Fuel Level Sensor Replacement in Engine Controls. Did you complete the replacement? | -- | Go to Step 11 | -- |
10 |
Important: Program the replacement PCM. Replace the PCM. Refer to Powertrain Control Module Replacement in Engine Controls. Did you complete the replacement? | -- | Go to Step 11 | -- |
11 |
Does the DTC reset? | -- | Go to Step 2 | System OK |
