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Ask Chad Farhat Your Own Question
Chad Farhat
Chad Farhat, ASE Certified Technician A6 - Electrical / Electronic systems A7 Heating / Air conditioning systems
Category: Chevy
Satisfied Customers: 1547
Experience:  Owner at Carolina Auto Service & Sales , 20 years Experience in Foreign & Domestic vehicles A6 - Electrical / Electronic systems A7 Heating / Air Conditioning systems
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I have four codes that came up, 1) p1781, I have four codes

Customer Question

Hello, I have four codes that came up, 1) p1781
JA: Just to clarify, what's the exact code? And have you tried to reset it?
Customer: Hello I have four codes that came up, 1) p1781, 2) p0118 3) p0700, 4) p0125, can you tell me what needs to be fixed on my car, for one it rev's up when I start it, the engine light is on, and it rumbles while I'm driving,, please help
JA: What is the model/year of your Chevy?
Customer: 2004 chevy aveo
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: bought a part that they told me I need , coolent temp sensor, I have to find someone to fix it I'm a female who can only change a tire,,,
JA: Anything else you think the mechanic should know?
Customer: no
Submitted: 3 months ago.
Category: Chevy
Expert:  Chad Farhat replied 3 months ago.

Hi, I'm Chad. Welcome to JustAnswer. I'm reviewing your question and I will be posting your reply ASAP.

Expert:  Chad Farhat replied 3 months ago.

hey, I m sorry you are having this problem

1- The p0118 is the ECT (engine coolant temp sensor and it needs to be replaced , if the wiring to it is good , it is fairly expensive, so changing it will be good idea since you bought already, the engine computer need the input from this sensor to operate correctly

2- The p0125 is a collateral code because of the p0118, telling the computer dont see the temp rising and it will not enter closed loop statu ,in turn will make you spend more gas and the engine will run rough,idle high,etc.. trying to balance the a/f ratio .

so this good hopefully will go away after replacing the ect sensor

3- the p0700 code is a transmission malfunction detected and the p1718 is , no speed input to transmission , so that could be a VSS Vehicle speed sensor , but is the car shifting good .

4- if none of the above fix it and the sensors are good and wiring, then it could and ecm or tcm module causing all this , but testing is needed

5- Check for vacum lines and vacuum leaks ,open hood and look around the engine bay area.

so lets starts by replacing The ECT sensor and clear codes and go from there .

please let me know

Thank You *****
ASE Certified Technician

2004 Chevrolet Aveo L4-1.6L VIN 6

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DTC P0118 CIRCUIT DESCRIPTION The engine coolant temperature (ECT) sensor is a variable resistor that measures the temperature of the engine coolant. The engine control module (ECM) supplies 5 volts to the ECT signal circuit and supplies a ground to the low reference circuit. If the ECM detects an excessively high ECT signal voltage, which is a low temperature indication, this DTC sets.

The table illustrates the difference between temperature, resistance, and voltage: DTC DESCRIPTOR This diagnostic procedure supports the following DTC: DTC P0118 Engine Coolant Temperature (ECT) Sensor Circuit High Voltage CONDITIONS FOR RUNNING THE DTC The engine is running for more than 60 seconds. CONDITIONS FOR SETTING THE DTC The ECM detects that the ECT sensor is less than -39°C (-38°F) for more than 6 seconds. ACTION TAKEN WHEN THE DTC SETS - The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. - The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records. CONDITIONS FOR CLEARING THE MIL/DTC - The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. - A current DTC, Last Test Failed, clears when the diagnostic runs and passes. - A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. - Clear the MIL and the DTC with a scan tool. DIAGNOSTIC AIDS - Test the ECT sensor at various temperature levels in order to evaluate the possibility of a skewed sensor. A skewed sensor can result in a driveability condition. - If the vehicle has set overnight, the ECT sensor and the intake air temperature (IAT) sensor values should display within 3°C (5°F). Refer to Temperature vs Resistance. - For an intermittent condition, refer to Intermittent Conditions. See: Computers and Control Systems > Initial Inspection and Diagnostic Overview > Intermittent Conditions

DTC P0125 CIRCUIT DESCRIPTION The engine control module (ECM) monitors the temperature of the engine coolant for engine control and as an enabling criteria for some diagnostics. The amount of air flow into an engine is proportional to the amount of heat an engine generates. The ECM monitors the amount of air flow into the engine to calculate engine coolant temperature (ECT). The ECM uses the calculated temperature to determine if the engine has warmed up to the closed loop temperature. If the coolant temperature does not increase normally or does not reach the closed loop temperature, diagnostics that use the ECT as enabling criteria, may not run when expected. If the engine coolant temperature fails to reach the closed loop temperature, before a predetermined amount of air flow enters the engine, this DTC sets. DTC DESCRIPTOR This diagnostic procedure supports the following DTC: DTC P0125 Engine Coolant Temperature (ECT) Insufficient for Closed Loop Fuel Control

DTC P0700 CIRCUIT DESCRIPTION This diagnostic trouble code (DTC) indicates that an emission related transmission DTC set in the transmission control module (TCM). The engine control module (ECM) receives the TCM DTC information over the serial data circuit. The ECM turns ON the malfunction indicator lamp (MIL) when the TCM sends a message over the serial data circuit requesting MIL illumination. The ECM will also store the freeze frame/failure records data for a transmission DTC. The DTC information for the ECM will only display DTC P0700, but the freeze frame/failure records data will display the transmission DTC that set. DTC DESCRIPTOR This diagnostic procedure supports the following DTC: DTC P0700 Transmission Control Module (TCM) Requested MIL Illumination CONDITIONS FOR RUNNING THE DTC DTC P0700 runs continuously CONDITIONS FOR SETTING THE DTC The ECM receives a serial data message, from the TCM, in order to illuminate the MIL. ACTION TAKEN WHEN THE DTC SETS - The control module illuminates the malfunction indicator lamp (MIL) when the diagnostic runs and fails. - The control module records the operating conditions at the time the diagnostic fails. The control module stores this information in the Freeze Frame/Failure Records. CONDITIONS FOR CLEARING THE MIL/DTC - The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail. - A current DTC, Last Test Failed, clears when the diagnostic runs and passes. - A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. - Clear the MIL and the DTC with a scan tool.

DTC P1718 Circuit Description

Conditions for Setting the DTC - Transmission control module (TCM) detects that malfunction of engine speed signal for 2 seconds - No DTC U2105 - Engine Misfire Detected Action Taken When the DTC Sets - TCM will request the illumination of the malfunction indicator lamp (MIL) and store the DTC when the TCM detects a failure on the 1st ignition cycle - No engine torque reduction control - No lock-up - No engagement pressure control - No 4th gear - No self-learning control - No timing solenoid control for N-D - TCM judges the engine revolution is 0 RPM Conditions for Clearing the DTC - The TCM turns OFF the MIL when no further failures are detected on the next ignition cycles. - The scan tool can clear the DTC from the TCM history. - The TCM clears the DTC from the TCM history memory after 40 consecutive ignition cycles without fault. Cause of Failure - Wiring harness or connector between engine control module (ECM) and TCM - ECM - TCM

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