DTC P1291: NO TEMPERATURE RISE SEEN FROM INTAKE AIR HEATERS

Monitor & Set Conditions

Temperature rise from intake air heaters is monitored for first 15 seconds of engine operation. DTC may be stored if initial Intake Air Temperature (IAT) sensor reading is 0-66°F (-17.8 to 18.8°C), Battery Temperature Sensor (BTS) and IAT sensor are within 10°F of each other, time between end of preheat and engine run state is less than 30 seconds, engine is cranked for less than 5 seconds before engine starts, preheat is completed before engine starts, post-heat is active and no IAT sensor or intake air heater relay DTCs exist.

Possible Causes

• Good Trip Counter Change To Zero
• DTC Equal To Freeze Frame
• Technical Service Bulletins (TSB) Or Hotline Bulletins
• Battery Cable High Resistance
• Intake Air Heater Feed High Resistance
• Intake Air Heater No. 2 Relay
• No. 2 Intake Air Heater
• No. 1 Intake Air Heater Feed High Resistance
• Intake Air Heater No. 1 Relay
• No. 1 Intake Air Heater

Testing

1. Turn ignition on with engine off. Using DRBIII(R) scan tool, check for DTCs. If Good Trip Counter for DTC P1291 is displayed and equal to zero, go to next step. If Good Trip Counter for DTC P1291 is displayed and not equal to zero, go to step 5 .

2. Ensure ignition is on with engine off. Using DVOM, check and record voltage across battery terminals. Continue monitoring battery voltage while using scan tool to briefly actuate intake air heater No. 1. DO NOT actuate intake air heater No. 1 for any longer than possible, as intake air heater draws a large amount of current. Stop actuation of intake air heater No. 1. If battery voltage drops .5 volt or greater when intake air heater No. 1 is actuated, go to next step. If battery voltage drops less than .5 volt when intake air heater No. 1 was actuated, go to step 13 .

3. Ensure ignition is on with engine off. Using DVOM, check and record voltage across battery terminals. Continue monitoring battery voltage while using scan tool to briefly actuate intake air heater No. 2. DO NOT actuate intake air heater No. 2 for any longer than possible, as intake air heater draws a large amount of current. Stop actuation of intake air heater No. 2. If battery voltage drops .5 volt or greater when intake air heater No. 2 is actuated, go to next step. If battery voltage drops less than .5 volt when intake air heater No. 2 was actuated, go to step 10 .

4. Ensure ignition is on with engine off. Using scan tool, check for DTCs and record FREEZE FRAME data. Try to duplicate conditions recorded in FREEZE FRAME data. Using scan tool, check for DTCs. If Good Trip Counter for DTC P1291 changes to zero, go to step 9 . If Good Trip Counter for DTC P1291 does not change to zero, conditions required for DTC to be stored are not present at this time. Possible causes are IAT sensor, intake air heater relay, intake air heater element or high resistance cables. Test is complete.

5. Ensure ignition is on with engine off. Using scan tool, determine if DTC matches FREEZE FRAME DTC. If DTC is equal to FREEZE FRAME DTC, go to next step. If DTC is not equal to FREEZE FRAME DTC, freeze frame DTC is a higher priority DTC and should be diagnosed before diagnosing DTC P1291. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .

6. Ensure ignition is on with engine off. Using scan tool, check for DTCs and record FREEZE FRAME data. Try to duplicate conditions recorded in FREEZE FRAME data. Using scan tool, check for DTCs. If Good Trip Counter for DTC P1291 changes to zero, go to next step. If Good Trip Counter for DTC P1291 does not change to zero, conditions required for DTC to be stored are not present at this time. Possible causes are IAT sensor, intake air heater relay, intake air heater element or high resistance cables. Test is complete.

7. Using DVOM, check and record voltage across battery terminals. Continue monitoring battery voltage while using scan tool to briefly actuate intake air heater No. 1. DO NOT actuate intake air heater No. 1 for any longer than possible, as intake air heater draws a large amount of current. Stop actuation of intake air heater No. 1. If battery voltage drops .5 volt or greater when intake air heater No. 1 is actuated, go to next step. If battery voltage drops less than .5 volt when intake air heater No. 1 was actuated, go to step 13 .

8. Using DVOM, check and record voltage across battery terminals. Continue monitoring battery voltage while using scan tool to briefly actuate intake air heater No. 2. DO NOT actuate intake air heater No. 2 for any longer than possible, as intake air heater draws a large amount of current. Stop actuation of intake air heater No. 2. If battery voltage drops .5 volt or greater when intake air heater No. 2 is actuated, go to next step. If battery voltage drops less than .5 volt when intake air heater No. 2 was actuated, go to step 10 .

9. Problem is intermittent. Turn ignition off. Inspect Engine Control Module (ECM) harness connector for corroded, pushed out or damaged terminals. ECM is located on driver's side of engine, just in front of fuel transfer pump and contains a 50-pin connector. Inspect wiring harness and connectors between ECM and intake air heater relays for chafed, pierced or partially broken wires. Inspect battery cables between batteries and intake air heater relays, and cables between intake air heater relays and intake air heater assembly. Intake air heater relays are located on bracket near driver's side battery. Intake air heater assembly is located on top of intake manifold. If terminals are not corroded, pushed out or damaged and wiring and cables are okay, check for Technical Service Bulletins (TSB) that may apply. If terminals are corroded, pushed out or damaged, or wiring or cables are damaged, repair as necessary.

10. Ensure ignition is on with engine off. Perform voltage drop test on battery cable that goes from battery to intake air heater relay No. 2. Intake air heater relay No. 2 is located on bracket near driver's side battery. If voltage drop on battery cable is .1 volt or less, go to next step. If voltage drop on battery cable is greater than .1 volt, replace battery cable.

11. Ensure ignition is on with engine off. Check cable that goes from intake air heater relay No. 2 to intake air heater No. 2 for excessive resistance by checking voltage drop on the cable. Intake air heaters No. 1 and 2 are incorporated into intake air heater assembly located on top of intake manifold. Intake air heaters may also be referred to as intake manifold air heaters. If voltage drop on cable is .1 volt or less, go to next step. If voltage drop on cable is greater than .1 volt, replace cable.

12. Ensure ignition is on with engine off. Connect DVOM between ground and output terminal on intake air heater relay No. 2. This is the terminal that the cable is attached to that goes to intake air heater No. 2. If voltage is greater than 12 volts, intake air heater No. 2 is defective. Replace intake air heater assembly. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. If voltage is 12 volts or less, replace intake air heater relay No. 2. See appropriate REMOVAL, OVERHAUL & INSTALLATION article.

13. Ensure ignition is on with engine off. Perform voltage drop test on battery cable that goes from battery to intake air heater relay No. 1. Intake air heater relay No. 1 is located on bracket near driver's side battery. If voltage drop on battery cable is .1 volt or less, go to next step. If voltage drop on battery cable is greater than .1 volt, replace battery cable.

14. Ensure ignition is on with engine off. Check cable that goes from intake air heater relay No. 1 to intake air heater No. 1 for excessive resistance by checking voltage drop on the cable. Intake air heaters No. 1 and 2 are incorporated into intake air heater assembly located on top of intake manifold. Intake air heaters may also be referred to as intake manifold air heaters. If voltage drop on cable is .1 volt or less, go to next step. If voltage drop on cable is greater than .1 volt, replace cable.

15. Ensure ignition is on with engine off. Connect DVOM between ground and output terminal on intake air heater relay No. 1. This is the terminal that the cable is attached to that goes to intake air heater No. 1. If voltage is greater than 12 volts, intake air heater No. 1 is defective. Replace intake air heater assembly. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. If voltage is 12 volts or less, replace intake air heater relay No. 1. See appropriate REMOVAL, OVERHAUL & INSTALLATION