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Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe® Online for applicable fixes to the calibration stored in the ECM. If necessary, recalibrate the ECM.

This fault code will only become active if the Maintenance Monitor is enabled in INSITE™ electronic service tool. Make sure that the oil and filter are changed before clearing the fault.

Possible repairs:

1)Change the engine lubricating oil and filter.

Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe® Online for applicable fixes to the calibration stored in the ECM. If necessary, recalibrate the ECM.

This fault code is logged when the ECM detects a turbocharger speed that is greater than the speed that is physically achievable by the turbocharger. Usually this indicates a faulty sensor or incorrect speed signals from the turbocharger speed sensor. This fault can be caused by failures in the following components:

1)Turbocharger speed sensor
2)Engine harness
3)ECM power supply or grounds
4)Electronic vehicle accessories which emit excessive electromagnetic interference.

This fault becomes inactive any time the ECM detects a valid turbocharger speed. If the fault occurs intermittently:

1)Look for causes of intermittent open circuit or short circuits in the turbocharger speed sensor circuit (including the speed sensor pigtail connector)
2)Look for sources of electronic noise such as poorly installed vehicle electronic components
3)Be sure that the vehicle chassis grounds are in good condition
4)Be sure that the ECM power supply and ground circuits are in good condition and that this power supply is not shared with other vehicle electronics.

Possible repairs:

1)Repair or replace the damaged connector or turbocharger speed sensor.
2)Replace the turbocharger speed sensor.
3)Repair or replace the engine harness or connector(s).
4)Replace the ECM.

Verify the ECM calibration is correct. Check the calibration revision history found on QuickServe™ Online for applicable fixes to the calibration stored in the ECM. If necessary, calibrate the ECM.

This fault can possibly come active if the ECM senses engine speed while at the same time a turbocharger speed signal is less than 600 rpm.

Possible causes:

1)Damaged turbocharger speed sensor
2)Damaged engine harness
3)Damaged alternator (EMI or internal short)
4)Damaged ECM.

This fault becomes inactive any time the speed signal from the turbocharger speed sensor returns.

If the fault occurs intermittently, look for causes of intermittent open or short circuits in the turbocharger speed sensor circuit (including the speed sensor pigtail connector).

For the code to clear, the ratio of boost pressure to ambient pressure must be above 1.19:1 for at least 30 consecutive seconds. This condition can only be achieved during a test drive when the engine is under load. Operating the engine at idle or high idle while stationary will not create enough load to maintain boost pressure at 1.19 times ambient pressure for 30 consecutive seconds.

Although it is possible for a damaged ECM to be the root cause of this fault code, it is highly unlikely and ECM replacement should only be considered as a last resort if no other repairs are successful in clearing the fault code.

In very rare cases, it has been shown that the turbocharger can cause this fault code to come active and turbocharger replacement may be the only way to clear the fault code.

Possible repairs:

1)Replace the turbocharger speed sensor.
2)Replace the alternator.
3)Replace the ECM.

Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe® Online for applicable fixes to the calibration stored in the ECM. If necessary, recalibrate the ECM.

Fault code 688 indicates that the oil level in the engine is much higher than the recommended oil level.

Other causes of fault code 688 may include:

1)The engine may have been overfilled with oil during the most recent oil change.
2)The fuel system may be leaking into the lube oil system. Check for fuel system faults or use fluorescent fuel system dye to identify leaks.
3)The cooling system may be leaking into the lube oil system. Check for coolant in the oil.

Possible repairs:

1)Correct the engine lubricating oil level condition.

Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe™ Online for applicable fixes to the calibration stored in the ECM. If necessary, recalibrate the ECM.

This fault is logged when the ECM does not receive a valid crankshaft position signal.

Possible causes:

1)Open or short circuit of the 5 volt SUPPLY, SIGNAL, or RETURN wire in the engine harness
2)Damaged crankshaft position sensor.

Possible repairs:

1)Replace the engine wiring harness.
2)Replace or shim the sensor if air gap is out of specification. If the target runout is excessive, replace the target.
3)Replace the crankshaft position sensor.
4)Replace the ECM.

Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe™ Online for applicable fixes to the calibration stored in the ECM. If necessary, calibrate the ECM.

The turbocharger inlet air temperature sensor shares return wires in the engine harness with other sensors. An open return can cause multiple fault codes to be active. Before troubleshooting Fault Code 691, check for multiple fault codes. An extension harness between the main engine harness and the turbocharger compressor inlet temperature sensor can be used depending on the turbocharger arrangement.

On ISB with CM2150 engines, an extension harness between the main harness and the ambient air temperature/pressure sensor is always used.

Possible causes:

1)Open return circuit in the harness, connectors, or sensor
2)Open signal circuit or short circuit to a voltage source
3)Damaged sensor.

Possible repairs:

1)Replace the turbocharger compressor inlet air temperature sensor.
2)Replace the ECM.
3)Repair or replace the engine harness.

Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe® Online for applicable fixes to the calibration stored in the ECM. If necessary, recalibrate the ECM.

An extension harness between the main engine harness and the turbocharger compressor inlet temperature sensor can be used, depending on the turbocharger arrangement.

On ISB with CM2150 engines, an extension harness between the main harness and the ambient air temperature/pressure sensor is always used.

Possible causes:

1)Signal circuit shorted to ground in the harness
2)Signal circuit shorted to return or ground in the sensor
3)Damaged sensor.

Possible repairs:

1)Replace the turbocharger compressor inlet air temperature sensor.
2)Replace the ECM.
3)Repair or replace the engine harness.
4) The removal and installation of the connector may correct the problem.

Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe® Online for applicable fixes to the calibration stored in the ECM. If necessary, recalibrate the ECM.

This sensor is located internally to the ECM. No troubleshooting is possible for this fault code. If the fault code is active, the ECM must be replaced.

Possible repairs:

1)Replace the ECM.

Verify the electronic control module (ECM) calibration is correct. Check the calibration revision history found on QuickServe® Online for applicable fixes to the calibration stored in the ECM. If necessary, recalibrate the ECM.

The ECM monitors the position of the missing tooth on the crankshaft speed sensor target and the camshaft speed sensor target. If the two positions do not match, the ECM then determines that there is a mechanical misalignment between the two sensors.

This fault code is logged when there is a mechanical misalignment between the crankshaft engine position sensor and the camshaft engine position sensor.

Possible causes:

1)Engine speed sensor rings that are loose or not aligned correctly
2)Mechanical misalignment.

Possible repairs:

1)Replace the position or speed sensor.
2)Replace the tone wheel.
3)Replace, tighten, or clean the ground wires or connections.
4)Remove and install camshaft to properly align timing marks at TDC.
5)Replace the crankshaft assembly if all steps have been completed and checked again.