Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
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HOMESERVICE MANUALSCHEVROLET2008HHR LT, 2.4 P, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT VARIANT/TRIMSECTION 7 (ENGINE CONTROLS AND FUEL - 2.0L - DTC P0010 TO DTC P0238)DTC P0121, P0122, OR P0123CIRCUIT/SYSTEM TESTING
2008 Chevrolet HHR LT, 2.4 P, Automatic
Circuit/System Testing
2008 Chevrolet HHR LT, 2.4 P, AutomaticSECTION Circuit/System Testing
WARNING: This page is about a different variant/trim than selected.
- Ignition OFF, disconnect the harness connector at the throttle body. Allow sufficient time for the ECM to completely power down.
- Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal C and ground.
- If greater than 5 ohms, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
- Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal E and ground.
- If less than 4.8 volts, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
- If greater than 5.2 volts, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.
- Verify the scan tool TP sensor 1 voltage is less than 0.1 volt.
- If greater than 0.1 volt, test the signal circuit terminal D for a short to voltage. If the circuit tests normal, replace the ECM.
- Install a 3A fused jumper wire between the signal circuit terminal D and the 5-volt reference circuit terminal E of the TP sensor 1, verify the TP sensor 1 voltage is greater than 4.8 volts.
- If less than 4.8 volts, test the TP sensor 1 signal circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
- Ignition OFF, disconnect the harness connector at the ECM.
- Test for less than 5 ohms of resistance on the TP sensor circuits between the following terminals:
- ECM C1 5-volt reference circuit terminal 39 to terminal E.
- ECM C1 signal circuit terminal 90 to terminal D.
- If greater than 5 ohms, repair the affected circuit.
- Test for infinite resistance between TP sensor 1 signal circuit terminal D and TP sensor 2 signal circuit terminal F.
- If less than infinite resistance, repair the short between TP sensor 1 signal circuit and TP sensor 2 signal circuit.
- If all circuits test normal, replace the throttle body.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.