Heater System Electrical Problem

DTC P1166: Electrical Problem in Primary HO2S (Sensor 1) Heater Circuit
1. Do the ECM/PCM Reset Procedure.
2. Start the engine.
Is DTC P1166 indicated?
YES-Go to step 3.
NO-Intermittent failure, system is OK at this time.
Check for poor connections or loose wires at C102 (located under the under-hood fuse/relay box), Primary HO2S relay, the Primary HO2S (Sensor 1) and the ECM/PCM.




3. Measure voltage between ECM/PCM connector terminals B19 and B20, 30 seconds after the ignition switch is turned ON (II).
Is there battery voltage?
YES-Substitute a known-good ECM/PCM and recheck. If the symptom/indication goes away, replace the original ECM/PCM.
Diagnostic Strategies

NO-Go to step 4.




4. Measure voltage between ECM/PCM connector terminals C13 and B20.
IS there battery voltage?
YES-Go to step 5.
NO-Go to step 9.
5. Turn the ignition switch OFF.
6. Disconnect the ECM/PCM connector B (25P).
7. Turn the ignition switch ON (II).




8. Measure voltage between ECM/PCM connector terminals B19 and B20.
Is there battery voltage?
YES-Substitute a known-good ECM/PCM and recheck. If the symptom/indication goes away, replace the original ECM/PCM.
Diagnostic Strategies

NO-Repair open or short in the wire between Primary HO2S (Sensor 1) and ECM/PCM (B19).
9. Turn the ignition switch OFF.
10. Disconnect the ECM/PCM connector C (25P) and the Primary HO2S (Sensor 1) 4P connector.




11. Check for continuity between the Primary HO2S (Sensor 1) 4P connector terminal No.3 and body ground.
Is there continuity?
YES-Repair short in the wire between Primary HO2S relay, Primary HO2S (Sensor 1) and ECM/PCM (C13).
NO-Go to step 12.
12. Turn the ignition switch ON (II).




13. Measure voltage between ECM/PCM connector terminals B16 and B20
Is there battery voltage?
YES-Repair open in the wire between the ECM/PCM (C1,A8*) and the Primary HO2S (Sensor 1) or Secondary HO2S (Sensor 2)*.
NO-Go to step 14.
14. Check the following fuses:
- POWER SEAT (20 A) fuse in under-hood fusel relay box.
- No.4 ECU (ECM/PCM) CRUISE CONTROL (15 A) fuse in driver's under-dash fuse/relay box.
- No.6 LAF HEATER (20 A) in passenger's under- dash fuse/relay box.

Are any of the fuses blown?
YES-Repair short in the wire between the Primary HO2S relay and the fuses.
NO-Go to step 15.
15. Check for continuity in the wires between the primary HO2S relay and the fuses.
Is there continuity?
YES-The wires are OK, replace the primary HO2S relay.
NO-Repair open in the wire between the primary HO2S relay and the fuses.