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Reductant Tank Temperature Sensor
Troubleshooting Guide (UQLS) - US17 Emissions
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Internal Content

Trouble shooting guide for diagnosing the Reductant Tank Temperature
Sensor (UQLS), commonly referred to as the DEF Level Sensor.
Fault
Code
P205B64

P203A13
P203C00
P206A13
P206C00
P206B64
P205A13
P205C00

Fault Description

Comments

Reductant Tank Temperature
Sensor Circuit
Range/Performance

If active and repeating, then
the sensor is faulty.

Reductant Level Sensor "A"
Aftertreatment Reagent Level
Short Circuit Low
Reductant Quality
Reductant Quality Sensor Low
Reductant Quality Sensor
Range/Performance
Reductant Tank Temperature
Sensor, Open Circuit
Aftertreatment Reagent Tank
Temperature Short Circuit Low

Internal sensor faults. If
active or confirmed, follow
the diagnostic steps below.
DEF Quality Low or High
(Most likely Sensor)
Internal sensor fault.
Replace sensor if sensor is
active or confirmed

If any of the above faults (orange or red rows) are present on a
DTC read out as active or confirmed follow the steps below.
Inactive faults require no further action.
1. Check the sensor wiring harness connection.
• Disconnect the harness and make sure there is no damage to
the wires or pins, corrosion, or water ingress in either of
the connectors. If damage is found replace in accordance with FSB
258-040.

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2. Verify the DEF quality is at an acceptable value.
NOTE: Use refractometer P/N 88890105 to verify the DEF quality. See
illustration below.

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3. Verify that the DEF tank is not frozen.
4. Ensure that the DEF tank is adequately filled.
5. Clear the Fault Codes.
6. Start the engine. Run the engine on high idle for 2 minutes at 1000
rpm or higher.
7. Turn the Engine Off, Key Off for 15 seconds.
8. Start the engine. Run the engine on high idle for 2 minutes a second
time.

Evaluate the Results:
• If any of the faults in red or orange above return active: Replace
the UQLS in accordance with FSB 258-040.
• If no faults in red or orange above return: No troubleshooting or

replacement of the UQLS is necessary.

If any of the faults in the green chart below are active follow the
directions in the Comments column.
DO NOT replace the sensor for any of these codes. None of these
codes immediately indicate a faulty component.

Fault
Code

Fault Description

Comments

DEF level low (Possible derate
P203F00 Reductant Level Low condition). Commonly low DEF quanity
or float stuck.
P203B00

Aftertreatment
Reagent Level
Warning

Lost Communication
U02A200
with Reductant
Quality Module
P24FF00

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Reductant
Temperature Too
High

System fault. Follow diagnostics.
Commonly a wiring harness or
connection issue.
DEF tank temp above 70°C (160°F).
Commonly the coolant lines to the DEF
tank are swapped.
DEF quality low and SCR efficiency low

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P207F00

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Reductant Quality

DEF quality low and SCR efficiency low.
Commonly a DEF quality issue.

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Tags

mack
def quality

volvo

p205b64

p206b64

def level sensor

u02a200

p206c00

p203b00

p24ff00

p203c00

p206a13

p205a13

uqls

p203a13
p207f00
p205c00

p203f00

Related links and attachments
FSB 258-040

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