Erratic Fuel Gauge Operation DTCs P2066 And/Or P2636 - keywords cluster empty gage inaccurate inoperative instrument IPC needle panel dender tank

This PI was superseded to update the information that step 5 is always performed. Please discard PIC4765.

The following diagnosis might be helpful if the vehicle exhibits the symptom(s) described in this PI.

Some customers may comment that the Fuel gauge goes to empty when the fuel level is greater than what is shown on the gauge and DTCs P2066 and P2636 are present. When these codes are present the Fuel Level Low message should be displayed on the DIC. This could be caused if the ECM does not receive the expected voltage signal to indicate that the fuel transfer is properly occurring. If this condition exists for 30 minutes both of these DTCs will be set. The fuel level sensor card may have slight discoloration possibly caused by fuel contamination which can affect the level sensor output. The fuel level sensor diagnostics are sensitive to this issue.

1. Verify that P2066 and P2636 DTC are set.
2. Confirm fuel rail pressure with the fuel pump on is 58-62 psi. If the pressure is not within this range, follow eSI Service Procedures to correct the issue and then proceed to Step 5.
3. Confirm proper jet pump transfer by checking and recording the fuel level sensor voltages using a Tech2. This must be performed with less than 3/4 tank of fuel. If required, remove sufficient fuel from the Schrader valve on the fuel rail. Follow all safety procedures as outlined in SI. Clear the DTCs to get a reading on the fuel gage. If the secondary (passenger side) sender is less than 2.2 volts and the primary (driver side) is more than .86 volts, the secondary (passenger side) level sensor and the module (includes the jet pump) should be replaced. Prior to replacing fuel hardware confirm all wiring connections are fully seated and harnesses are properly routed. After replacing the level sensor and module move to step 5.
4. If the jet transfer pump is operating properly the fuel sender card may be contaminated. This could cause an incorrect voltage signal to be sent to the ECM. Customers should be advised to correct a contamination issue by adding one bottle of GM Fuel System Treatment PLUS (part number 88861011) to the fuel system on their next fuel fill. Note; the fuel level must be below ¼ tank when the fuel treatment is added. The treatment rate is 1 oz. per gallon of fuel (Using one 20 oz bottle to the fuel system is acceptable). To clean a severely contaminated fuel level sensor, it is permissible to treat the fuel system on two consecutive tanks.

Note: Back to back treatment is only permitted once in the life of the vehicle. After the initial treatment, customers should be advised to add one bottle of GM Fuel System Treatment PLUS to the fuel tank at every oil change, however, not more frequently than once every 3000 miles. Proceed to step 5

5. A revised ECM calibration 12624797 is available through TIS2WEB under the fuel system heading. To reflash the ECM please use labor operation L1199 @ .2 hours.

If the vehicle continues to have the concern after the calibration has been updated it is possible there is an intermittent jet transfer or an intermittent stuck float arm issue. Poor jet transfer could be due to an intermittent clog in the jet pump or a kinked transfer line in the either fuel tank.

Fuel contamination is discussed in service publication 05-00-89-078B and Top Tier Fuel is discussed in publication 05-06-04-022D. These documents should be provided to customers if they have questions regarding fuel quality. E85 fuel requirements are reviewed in publications 06-06-04-035A and 05-06-04-035C. E85 must not be used in Corvettes.

Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.