Hummer H1 Service Manual page 315

5-116 Transmission/Transfer Case
DTC P1870 Transmission Component Slipping
Range Gear 1-2 Sol
1st On
2nd Off
Overdrive
3rd Off
4th On
A = Applied
H = Holding
* = Holding but not effective
O = Overrunning
Circuit Description
The PCM monitors the difference in engine speed and trans-
mission input speed. In D3 drive range with the converter
clutch engaged, engine speed should closely match transmis-
sion output speed. In D4 drive range with the converter clutch
engaged, clutch slip speed should be between -20 and +20 rpm.
This DTC detects excessive slip when the converter clutch is
engaged.
Conditions For Setting DTC
The following conditions are met for 10 seconds with 4th gear
commanded.
• No engine speed DTC P0335.
• No DTCs P0121, P0122, P0123, P0220,P0221, P0222,
P0223, P0225, P0226, P0227, P0228.
• No DTCs P0716 or P0717.
• No DTC P0722 or P0723.
• No DTCs P0741, P0742 or P0719.
• No shift solenoid 1-2 DTCs P0751 or P0753.
• No shift solenoid 2-3 DTCs P0756 or P0758.
• No DTC P1810.
• Gear range is D4.
• Throttle angle between 12% and 70%. Engine torque
between 60 and 280 ft/lbs.
• Fluid temperature is between -10°C and 130°C
(14° F and 266° F).
• Engine speed is between 1200 and 3750 rpm. Input
speed is between 40 and 205 rpm.
• Slip between +140 and +500 rpm is detected.
• Shift Solenoid performance counters are clear.
Action Taken When DTC Sets
• PCM will command maximum line pressure.
• PCM will inhibit converter clutch engagement.
Fourth Overrun
2-3 Sol Clutch Clutch
Off Ð Ð
Off Ð Ð
On Ð Ð
On A Ð
___________________________________________
O/D
Roller FWD Direct
Clutch Clutch Clutch
H A Ð
H A Ð
H A A
O A A
• PCM inhibits 4th gear if in hot mode.
• PCM will freeze shift adapts. PCM illuminates the
warning lamp.
Conditions For Clearing DTC
• For California vehicles, the PCM will turn the lamp off
after three consecutive ignition cycles without a failure
reported.
• The DTC can be cleared using the scan tool. The DTC
will be cleared when the vehicle has achieved 40 warm-
up cycles without a failure reported.
• The PCM will cancel the DTC default actions when the
fault no longer exists and the ignition is cycled "off"
long enough to power down the PCM.
Diagnostic Aids
• A pressure switch malfunction could set DTC P1870.
• A mechanical failure of the shift solenoids, or converter
clutch solenoid could set a DTC P1870.
• Internal transmission failures may result in a DTC
P1870.
• If any engine DTCs or TPS codes are present diagnose
and clear these DTCs first. Then check to see if the
transmission DTCs have reset.
Test Description
The numbers below refer to the step numbers on the diagnostic
chart.
1. This test checks the indicated range signal to the ac-
tual selected range. A faulty switch could set a DTC
P1870.
2. This test checks the torque converter for slippage
while in a commanded lock-up state.
Interm.
Front Sprag Interm.
Band Clutch Clutch
Ð * Ð
Ð H A
Ð O A
Ð O A
®
Lo
Roller Rear
Clutch Band
H Ð
O Ð
O Ð
O Ð