The P1516 is what's putting it in Reduced Power Mode.
Here's what the service manual says about it:
_____________
Circuit Description
The commanded throttle position, based on accelerator pedal position and possibly other limiting factors, is compared to the Actual throttle position. The 2 values should be within a calibrated range of each other. Both the PCM and the TAC module redundantly monitor the Commanded and Actual throttle position. This DTC sets if the TAC module detects the problem.
Conditions for Setting the DTC
* DTC P1518 is not set.
* The ignition switch is in the crank or run position.
* The ignition voltage is greater than 5.23 volts.
* Not in battery saver mode.
* The TAC module detects that the commanded and actual throttle positions are not within a calibrated range of each other or the PCM and the TAC cannot determine throttle position or both TP sensors are invalid.
* All above conditions met for less than 1 second.
Action Taken When the DTC Sets
* The PCM will illuminate the Malfunction Indicator Light (MIL) when this diagnostic runs and fails.
* The Reduced Engine Power message displays on the drivers information center.
* The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Freeze Frame and/or Failure Records.
* If no other TAC System DTCs are set, the TAC System will operate in Reduced Engine Power mode. If certain TAC System DTCs are set at the same time, the TAC System either defaults to a more tightly restricted mode of operation if the TAC determines that limited safe operation is possible, or the TAC commands the engine to shut down.
Conditions for Clearing the MIL/DTC
* The PCM turns the MIL OFF after three consecutive drive trips that the diagnostic runs and does not fail.
* A last test failed (Current DTC) will clear when the diagnostic runs and does not fail.
* A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
* The PCM battery voltage is interrupted.
*
Important
The clear DTC info function may have to be performed twice in order to clear a Throttle Actuator Control System DTC.
Clear the MIL/DTC information using a scan tool.
Diagnostic Aids
The following may cause an intermittent:
* Poor connections. Check for adequate terminal tension. Refer to Troubleshooting Procedures, Checking Terminal Contact (Body and Accessories/Wiring Systems) for proper procedure.
* Corrosion
* Mis-routed harness
* Rubbed through wire insulation
* Broken wire inside the insulation
* Inspect the TAC module connectors for signs of water intrusion. When this occurs, multiple DTCs should be set and no circuit or component problems can be located.
* For an intermittent condition refer to Symptoms .
* If a repair is completed and the DTC was cleared using a scan tool on the same ignition cycle, the default action will not clear until an ignition cycle has occurred.
* When the TAC module detects a problem within the TAC System, more than one TAC System related DTC may set. This is due to the many redundant tests run continuously on this system. Locating and repairing one individual problem may correct more than one DTC. Keep this in mind when reviewing captured DTC info.
Test Description
The numbers below refer to the step numbers on the diagnostic table.
5.
If the TP Indicated Angle does not follow the movement of the throttle blade, and no TP Sensor DTCs are set, there is a mechanical problem with the throttle shaft or the TP Sensor. Replace the throttle body assembly. Re-install the air inlet duct after you complete the repairs.
21.
When a problem is detected within the TAC System, more than one TAC System related DTC may set. This is due to the many redundant tests run continuously on this system. It is possible that locating and repairing one individual problem may correct more than one DTC. Keep this in mind when reviewing captured DTC info.
__________________
The C1278 is a sympathy code that usually accompanies any code that put the car in REP mode. When the P1516 set, the C1278 came with it.
The C1281 is a steering position sensor code, but since your 97 doesn't have Active Handling, I wouldn't worry too much about it.
And don't worry about the U codes either. They are almost always there.
